backend: add test for lyric

[vnghia]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 82.60870% with 40 lines in your changes missing coverage. Please review.

Project coverage is 76.06%. Comparing base (310e6d8) to head (cf6ca7a).
Report is 4 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
nghe-backend/src/file/lyric/mod.rs	86.61%	0 Missing and 19 partials ⚠️
...src/route/media_retrieval/get_lyrics_by_song_id.rs	0.00%	9 Missing ⚠️
nghe-backend/src/scan/scanner.rs	50.00%	0 Missing and 5 partials ⚠️
nghe-backend/src/file/audio/information.rs	57.14%	0 Missing and 3 partials ⚠️
nghe-backend/src/orm/lyrics.rs	93.10%	0 Missing and 2 partials ⚠️
nghe-backend/src/file/audio/extract/file.rs	66.66%	0 Missing and 1 partial ⚠️
nghe-backend/src/file/audio/extract/mod.rs	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #625      +/-   ##
==========================================
+ Coverage   74.71%   76.06%   +1.35%     
==========================================
  Files         185      185              
  Lines        5308     5407      +99     
  Branches     5308     5407      +99     
==========================================
+ Hits         3966     4113     +147     
+ Misses        804      730      -74     
- Partials      538      564      +26     

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