Add OpenTelemetry baggage observability

[vrslev]

Summary

• add an opt-in span processor that maps allowlisted W3C baggage keys to server and consumer span attributes
• add opt-in Sentry enrichment for searchable baggage tags and URL-encoded links
• preserve existing trace propagation and custom before-send callbacks
• document the generic settings and their output contract

Verification

• 56 focused OpenTelemetry and Sentry tests passed on Python 3.13
• Ruff format check passed
• Ruff lint check passed
• independent review: No material findings
• full local mypy was blocked by the pre-existing environment missing current optional FastMCP dependencies and an unrelated Litestar hook signature mismatch; the pull-request matrix is authoritative

Compatibility

All new settings default to empty collections, so existing consumers are unchanged until they opt in.

Delivery dependency

Downstream consumer updates remain pending until this package change is approved and released.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	98.77% <100.00%> (+0.61%)	⬆️

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Files with missing lines	Coverage Δ
...obootstrap/instruments/opentelemetry_instrument.py	98.48% <100.00%> (+0.19%)	⬆️
microbootstrap/instruments/sentry_instrument.py	97.70% <100.00%> (+10.37%)	⬆️

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