perf(weekly-report): Batch key errors Snuba query

[amy-chen23]

Resolves ID-1618

Summary

• Replace N per-project Snuba JOIN queries for key errors with a single batched org-wide query, reducing Snuba round-trips from N to ceil(N/100)
• Gate behind organizations:weekly-report-batched-key-errors feature flag with fallback to existing per-project path
• Chunk project IDs into batches of 100 to prevent query timeouts for large orgs

Context

The key_errors portion of weekly report generation is the slowest step. For each project in an org, it fires a separate events ⨝ group_attributes JOIN query to Snuba. For an org with 100 projects, that's 100 sequential round-trips.

This PR introduces a batched alternative: one query per 100 projects using project_id IN [...] and GROUP BY (project_id, group_id), then extracts top 3 per project in Python. For a 100-project org, this is 1 query instead of 100.

Test plan

• All 35 existing tests pass with flag off (old path)
• 2 new tests exercise the batched path (test_org_key_errors_batched, test_message_builder_filter_resolved_batched)
• ruff, mypy clean

[linear-code]

ID-1618

[amy-chen23]

• Chunk project IDs into batches of 100 to prevent query timeouts for large orgs

Arbitrarily picked 100 projects --> can increase/decrease if necessary

[shashjar]

query impl itself looks good to me, we can simplify by removing the EAP query path

[shashjar]

can we implement this as just a Snuba query to start? we can add the parallel EAP query later on

[shashjar]

seems like a useful comment to leave

[cvxluo]

nit: for typing, we typically type parameters as Sequence, etc. to be more general, and return the more specific list type

[cvxluo]

i notice that we have eap versions of the 'project key' variant of this function, do we need that here too?

[amy-chen23]

for now, we won't add the EAP versions. we'll add the parallel eap version in another PR (if needed)

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 4f0be31. Configure here.}