Materialize scoped baggage on current span

[vrslev]

Summary

• extend opentelemetry_baggage_scope with an optional, explicit baggage-to-span attribute mapping
• materialize supplied non-null values on an already-started recording span
• preserve existing baggage propagation, exception snapshotting, and caller compatibility

This complements BaggageSpanProcessor: the processor covers server and consumer spans created after baggage exists, while the scope covers spans that start before an authoritative value becomes available.

Verification

• just test tests/instruments/test_opentelemetry.py
• just lint-ci
• just test — 219 passed, 99% coverage
• git diff --check
• independent review: no material findings

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	99.01% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...obootstrap/instruments/opentelemetry_instrument.py	98.67% <100.00%> (+0.03%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.