feat: add audit_pass notification event

[ChrisJr404]

Description

Closes #5865.

Audit failures can already be sent to notification targets, but passes cannot, so there is no way to track successful audits through the notification system without re-running them via the Python API or writing a custom target that only ever sees failures.

This adds an AUDIT_PASS notification event. When a non-blocking or blocking audit runs and returns no failing rows, Scheduler._audit_snapshot now fires AUDIT_PASS in the same place it already fires AUDIT_FAILURE for failing audits. Skipped audits are neither a pass nor a failure, so they don't notify. The event carries the audit name and the model name.

Nothing changes by default. A target only receives these notifications if audit_pass is in its notify_on set, so existing configs behave exactly as before.

notification_targets:
  - type: slack_webhook
    url: ...
    notify_on:
      - audit_pass
      - audit_failure

Test plan

• Added a notify_audit_pass unit test covering the message with and without a model name.
• Extended test_audit_failure_notifications so the passing-audit case asserts AUDIT_PASS fires (global and to the owner) and the skipped case still fires nothing.
• ruff check, ruff format --check, and mypy clean on the changed files.
• pytest tests/core/test_notification_target.py tests/core/test_scheduler.py passes (27 tests).

Checklist

• I have run make style and fixed any issues.
• I have added tests for my changes.
• All existing tests pass.
• My commits are signed off per the DCO.

[StuffbyYuki]

@ChrisJr404 Thanks for this PR! No blocker but one thought: passing audit_name / model_name into send() the way failures already pass audit_error=? Let me know!