fix: make source group filtering strict

[AnannyaMahajan]

Summary

Make source group filtering strict when groups are explicitly configured.

Changes

• When sources.groups is set, only sources belonging to those groups are loaded
• Sources with empty or default groups are excluded unless explicitly listed
• Behavior remains unchanged when no groups are configured

Tests

• Updated existing tests to match strict filtering behavior
• Added coverage for group-limited source loading

Notes

• Change is limited to source filtering logic
• No impact on metrics, sinks, schema, or database behavior

Tests now pass after updating expectations for strict group filtering.

Note: running tests locally requires generating web assets
(internal/webui → npm install && npm run build), which CI already does.

[0xgouda]

Please 1. Fix failing tests 2. Add tests 3. Rewrite the PR description its too verbose

[AnannyaMahajan]

Please 1. Fix failing tests 2. Add tests 3. Rewrite the PR description its too verbose

Thanks for the review!

I’ve fixed the failing tests, updated test coverage for strict group filtering, and rewritten the PR description to be more concise.
Please let me know if anything else needs adjustment.

[coveralls]

Pull Request Test Coverage Report for Build 21074228430

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 5 of 7 (71.43%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 75.281%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/reaper/reaper.go	5	7	71.43%

Totals
Change from base Build 21071371678:	-0.02%
Covered Lines:	4014
Relevant Lines:	5332

---

💛 - Coveralls