Add Bugsnag instrumentation module

[morgan-wowk]

TL;DR

Adds a Bugsnag error reporting integration that is a no-op when the required environment variables are not set.

What changed?

A new bugsnag instrumentation module was introduced with three entry points:

• setup(service_name) — configures the Bugsnag client using environment variables (TANGLE_BUGSNAG_API_KEY, TANGLE_ENV, TANGLE_SERVICE_VERSION, TANGLE_BUGSNAG_NOTIFY_ENDPOINT, TANGLE_BUGSNAG_SESSIONS_ENDPOINT).
• notify(exception, **metadata) — reports an exception to Bugsnag with optional extra metadata attached.
• _before_notify(event) — a Bugsnag callback that automatically attaches contextual logging metadata (e.g. request_id, user_id) to every reported event under a tangle_context tab.

Both setup and notify are no-ops when TANGLE_BUGSNAG_API_KEY or TANGLE_ENV are missing. Failures within setup and notify are caught and logged rather than propagated.

How to test?

• Set TANGLE_BUGSNAG_API_KEY and TANGLE_ENV in your environment and call setup() followed by notify() with a test exception to verify events appear in Bugsnag.
• Run the unit tests: pytest tests/instrumentation/test_bugsnag.py

Why make this change?

To provide structured, centralized error reporting to Bugsnag across backend services, with automatic enrichment from contextual logging metadata and safe fallback behaviour when Bugsnag is not configured.

[morgan-wowk]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Add Bugsnag error grouping with stable normalized keys #234
• Wire Bugsnag into the orchestrator #232
• Wire Bugsnag into the API server #231
• Add Bugsnag instrumentation module #230 👈 (View in Graphite)
• Add bugsnag Python SDK dependency #229
• master

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