[DRAFT] Typing: remove mypy override for sentry.snuba.metrics.query_builder

[cursor]

Summary

• remove sentry.snuba.metrics.query_builder from the mypy override weak list in pyproject.toml
• add type narrowing/alias helpers in query_builder.py so the module passes strict typing
• tighten several internal annotations in query/result conversion paths to satisfy mypy without behavior changes

Testing

• PATH="/workspace/.venv/bin:$PATH" .venv/bin/python tools/mypy_helpers/mypy_without_ignores.py src/sentry/snuba/metrics/query_builder.py
• PATH="/workspace/.venv/bin:$PATH" DATABASE_URL="postgresql://postgres:postgres@127.0.0.1/sentry" SENTRY_SKIP_SERVICE_VALIDATION=1 .venv/bin/pytest -svv --reuse-db tests/sentry/snuba/metrics/test_query_builder.py
• PATH="/workspace/.venv/bin:$PATH" .venv/bin/prek run -q

@armenzg could you please review this draft PR?

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.