CmdPal: Prevent unsynchornized access to More commands (#46020)

## Summary of the Pull Request

This PR fixes a crash caused by unsynchronized access to a context menu:

- Fixes `System.ArgumentException: Destination array was not long
enough` crash in `CommandItemViewModel.AllCommands` caused by
`List<T>.AddRange()` racing with background `BuildAndInitMoreCommands`
mutations
- Replaces mutable `List<T>` public surfaces with immutable array
snapshots protected by a `Lock`; writers hold the lock, mutate the
backing list, then atomically publish new snapshots via `volatile`
fields that readers access lock-free
- Applies the same snapshot pattern to `ContentPageViewModel`, using a
bundled `CommandSnapshot` object for atomic publication (since
`PrimaryCommand` drives command invocation there, not just UI hints)
- Narrows `IContextMenuContext.MoreCommands` and `AllCommands` from
`List<T>`/`IEnumerable<T>` to `IReadOnlyList<T>` to prevent consumers
from casting back and mutating
- Moves `SafeCleanup()` calls outside locks in cleanup paths to avoid
holding the lock during cross-process RPC calls

<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] Closes: #45975 
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/ListItemViewModel.cs

@@ -159,7 +159,6 @@ public partial class ListItemViewModel : CommandItemViewModel
                 UpdateShowDetailsCommand();
                 break;
             case nameof(model.MoreCommands):
-                UpdateProperty(nameof(MoreCommands));
                 AddShowDetailsCommands();
                 break;
             case nameof(model.Title):
@@ -195,19 +194,27 @@ public partial class ListItemViewModel : CommandItemViewModel
             pageContext is ListViewModel listViewModel &&
             !listViewModel.ShowDetails)
         {
-            // Check if "Show Details" action already exists to prevent duplicates
-            if (!MoreCommands.Any(cmd => cmd is CommandContextItemViewModel contextItemViewModel &&
-                                        contextItemViewModel.Command.Id == ShowDetailsCommand.ShowDetailsCommandId))
+            var addedCommand = false;
+            lock (MoreCommandsLock)
             {
-                // Create the view model for the show details command
-                var showDetailsCommand = new ShowDetailsCommand(Details);
-                var showDetailsContextItem = new CommandContextItem(showDetailsCommand);
-                var showDetailsContextItemViewModel = new CommandContextItemViewModel(showDetailsContextItem, PageContext);
-                showDetailsContextItemViewModel.SlowInitializeProperties();
-                MoreCommands.Add(showDetailsContextItemViewModel);
+                // Check if "Show Details" action already exists to prevent duplicates
+                if (!UnsafeMoreCommands.Any(cmd => cmd is CommandContextItemViewModel contextItemViewModel &&
+                                                  contextItemViewModel.Command.Id == ShowDetailsCommand.ShowDetailsCommandId))
+                {
+                    var showDetailsCommand = new ShowDetailsCommand(Details);
+                    var showDetailsContextItem = new CommandContextItem(showDetailsCommand);
+                    var showDetailsContextItemViewModel = new CommandContextItemViewModel(showDetailsContextItem, PageContext);
+                    showDetailsContextItemViewModel.SlowInitializeProperties();
+                    UnsafeMoreCommands.Add(showDetailsContextItemViewModel);
+                    RefreshMoreCommandStateUnsafe();
+                    addedCommand = true;
+                }
             }
 
-            UpdateProperty(nameof(MoreCommands), nameof(AllCommands));
+            if (addedCommand)
+            {
+                UpdateProperty(nameof(MoreCommands), nameof(AllCommands));
+            }
         }
     }
 
@@ -222,22 +229,27 @@ public partial class ListItemViewModel : CommandItemViewModel
             pageContext is ListViewModel listViewModel &&
             !listViewModel.ShowDetails)
         {
-            var existingCommand = MoreCommands.FirstOrDefault(cmd =>
-                                        cmd is CommandContextItemViewModel contextItemViewModel &&
-                                        contextItemViewModel.Command.Id == ShowDetailsCommand.ShowDetailsCommandId);
-
-            // If the command already exists, remove it to update with the new details
-            if (existingCommand is not null)
+            CommandContextItemViewModel? oldCommand = null;
+            lock (MoreCommandsLock)
             {
-                MoreCommands.Remove(existingCommand);
+                oldCommand = UnsafeMoreCommands
+                    .OfType<CommandContextItemViewModel>()
+                    .FirstOrDefault(contextItemViewModel => contextItemViewModel.Command.Id == ShowDetailsCommand.ShowDetailsCommandId);
+
+                if (oldCommand is not null)
+                {
+                    UnsafeMoreCommands.Remove(oldCommand);
+                }
+
+                var showDetailsCommand = new ShowDetailsCommand(Details);
+                var showDetailsContextItem = new CommandContextItem(showDetailsCommand);
+                var showDetailsContextItemViewModel = new CommandContextItemViewModel(showDetailsContextItem, PageContext);
+                showDetailsContextItemViewModel.SlowInitializeProperties();
+                UnsafeMoreCommands.Add(showDetailsContextItemViewModel);
+                RefreshMoreCommandStateUnsafe();
             }
 
-            // Create the view model for the show details command
-            var showDetailsCommand = new ShowDetailsCommand(Details);
-            var showDetailsContextItem = new CommandContextItem(showDetailsCommand);
-            var showDetailsContextItemViewModel = new CommandContextItemViewModel(showDetailsContextItem, PageContext);
-            showDetailsContextItemViewModel.SlowInitializeProperties();
-            MoreCommands.Add(showDetailsContextItemViewModel);
+            oldCommand?.SafeCleanup();
 
             UpdateProperty(nameof(MoreCommands), nameof(AllCommands));
         }