Unpin sqlalchemy<2.1 once the OTel SQLAlchemy instrumentor supports 2.1 #60

Blocked by: a release of opentelemetry-instrumentation-sqlalchemy that includes open-telemetry/opentelemetry-python-contrib#5120 (merged 2026-10-14, not released yet).

Why the pin exists

pyproject.toml pins sqlalchemy[asyncio]<2.1. Every released opentelemetry-instrumentation-sqlalchemy up to 0.66b1 declares sqlalchemy >= 1.0.0, < 2.1.0. On SQLAlchemy 2.1, instrument() hits a DependencyConflict and does nothing, and lite-bootstrap silences the logger that reports it. With #59 the SQLAlchemy instrumentor is the only source of database spans, so upgrading would quietly drop all DB tracing.

Why it's worth doing

On our benchmark, SQLAlchemy 2.1.4 made ORM session.get about 20-30% faster than 2.0.54. Core queries and bulk inserts didn't change.

When unblocked

1. Upgrade opentelemetry-instrumentation-sqlalchemy to the release with SQLAlchemy 2.1 support.
2. Remove the <2.1 pin and run uv lock.
3. Run the full suite. tests/test_tracing.py fails if the instrumentor stops producing spans.