[DRAFT] Type sentry.snuba.metrics.query_builder and remove override

[cursor]

Summary

• Remove sentry.snuba.metrics.query_builder from the mypy "typing issues" override list in pyproject.toml
• Add explicit type narrowing/casts/annotations in query_builder.py so it passes strict mypy checks without disabled error codes
• Preserve runtime behavior while making action-by field handling and metric param typing explicit

Testing

• ✅ .venv/bin/python -m mypy src/sentry/snuba/metrics/query_builder.py
• ✅ .venv/bin/prek run -q
• ⚠️ make test-selective failed in this environment (gcloud missing)
• ⚠️ SENTRY_SKIP_SERVICE_VALIDATION=1 .venv/bin/pytest -n3 -svv --reuse-db tests/sentry/snuba/metrics/test_query_builder.py failed because local Redis/Postgres services are unavailable (localhost:6379 connection refused)

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

@armenzg could you review this draft PR?