Fix calculator appending extra zeros on non-en-US locales (#45624)

The C++ expression engine formatted results using the system locale,
which could produce comma decimal separators (e.g. "8,000000000000000").
The C# side then parsed this with en-US culture, interpreting commas as
thousands separators, turning 8 into 8000000000000000.

Fix: imbue the classic (C) locale on the output stream to always use
a dot decimal separator regardless of system locale.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/common/CalculatorEngineCommon/ExprtkEvaluator.cpp

@@ -28,6 +28,7 @@ namespace ExprtkCalculator::internal
     std::wstring ToWStringFullPrecision(double value)
     {
         std::wostringstream oss;
+        oss.imbue(std::locale::classic());
         oss << std::fixed << std::setprecision(15) << value;
         return oss.str();
     }