CMRT 24: DAO: Add getGroupsForMbid() and getAllGroupCandidates()

[Swarnadip-Kar]

Adds the two read-only lookups the CMRT grouping pipeline needs as its
first step, before any fingerprint comparison happens. Pure plumbing —
no behavior changes for anything that already exists.

getGroupsForMbid(mbid)

Returns every cmrt_group whose canonical track's library row has the given
musicbrainz_recording_id. Joins through canonical_track_id rather than
adding an mbid column to cmrt_groups, since that FK already exists and
the canonical track's MBID is exactly what we want anyway.

getAllGroupCandidates()

Returns every cmrt_group, unfiltered. Only meant for the no-MBID fallback
path (AcoustID found no match for the new track, so there's nothing to
pre-filter the SimHash scan with). Documented as such in the header so it
doesn't get reached for in the normal case by mistake.

MbidGroupCandidate

New DTO carrying just group_id, fingerprint_hash, and canonical_track_id.
Deliberately smaller than CmrtGroup -- the SimHash pre-filter step (CMRT 26)
only needs these three fields, not the MusicBrainz-sync or local_preferred
columns CmrtGroup also carries.

Notes for reviewers

• Neither method touches anything write-side; both are read-only and safe
  to call from the AcoustID worker thread.
• getAllGroupCandidates() will get slower as a library's group count grows,
  same caveat as any full-table scan. Acceptable for now since it's a
  fallback path, not the common case.

Depends on: CMRT Phase 1 (#32)

[coveralls]

Coverage Report for CI Build 27872292646

Warning

No base build found for commit 6eeb7ce on pr/cmrt-phase1-complete.
Coverage changes can't be calculated without a base build.
If a base build is processing, this comment will update automatically when it completes.

Coverage: 30.437%

Details

• Patch coverage: 56 uncovered changes across 1 file (0 of 56 lines covered, 0.0%).

Uncovered Changes

File	Changed	Covered	%
src/library/dao/trackfingerprintdao.cpp	56	0	0.0%

Coverage Regressions

Requires a base build to compare against. How to fix this →

---

Coverage Stats

Relevant Lines:	116230
Covered Lines:	35377
Line Coverage:	30.44%
Coverage Strength:	59272.14 hits per line

---

💛 - Coveralls