Match substrings fuzzily

[snejus]

Fixes #2043
Fixes #5638

Improve the fuzzy plugin in two ways:

1. Make short fuzzy queries behave more like substring matching.
2. Force fuzzy-prefixed queries to use slow evaluation so fuzzy logic is always applied.

Problem

Fuzzy prefix queries (for example ~foo or custom prefixes like %%foo) could take a fast DB query path on normal fields, which bypassed fuzzy semantics and produced broad/
unrelated matches #5638.

Also, when the query pattern was shorter than the field value, fuzzy matching was too strict for substring-style use cases #2043.

Thanks to @carreter for this in #5140. Opened a new PR since I did not have permissions to push to their fork.

Supersedes #5140.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.37%. Comparing base (bb08923) to head (48763ee).
⚠️ Report is 5 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6408      +/-   ##
==========================================
+ Coverage   69.33%   69.37%   +0.04%     
==========================================
  Files         141      141              
  Lines       18794    18801       +7     
  Branches     3061     3063       +2     
==========================================
+ Hits        13031    13044      +13     
+ Misses       5118     5111       -7     
- Partials      645      646       +1     

Files with missing lines	Coverage Δ
beetsplug/fuzzy.py	96.15% <100.00%> (+32.99%)	⬆️

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[Copilot]

Pull request overview

PR make fuzzy plugin better when query shorter than field, so user can do substring-ish fuzzy search (help for noisy titles like YouTube). Also add changelog note for Unreleased.

Changes:

• Scale fuzzy threshold by max possible ratio when len(pattern) < len(val).
• Use quick_ratio() as cheap gate before ratio() calc.
• Add changelog entry for fuzzy matching improvement.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docs/changelog.rst	Add Unreleased note for fuzzy plugin behavior change.
beetsplug/fuzzy.py	Adjust fuzzy matching logic to behave better for shorter queries.