constants.py subclassed opentelemetry.semconv.trace.SpanAttributes, which
is deprecated since semconv 1.25.0 (emits a DeprecationWarning; the pinned
0.63b1 has it live). Source the legacy span-attribute keys from the
non-deprecated _incubating attribute modules instead:
http.url / http.method / http.status_code <- _incubating http_attributes
db.name / db.statement / db.operation <- _incubating db_attributes
The stable http module renamed these (http.request.method, ...), so only
the incubating module preserves the original values. Custom keys
(db.instance/type/ip/port, error.*, result.*) stay literals.
Verified: emitted attribute keys are byte-identical before/after for every
key instrumentors.py reads, and importing constants no longer emits a
DeprecationWarning.