Fix escaped quote handling in PGN tag values

[CorentinGS]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.29%. Comparing base (abc72cb) to head (fe478c1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #114      +/-   ##
==========================================
+ Coverage   70.18%   70.29%   +0.10%     
==========================================
  Files          27       27              
  Lines        4166     4181      +15     
==========================================
+ Hits         2924     2939      +15     
  Misses       1110     1110              
  Partials      132      132              

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[Copilot]

Pull request overview

Adds support for the PGN spec's \" and \\ escape sequences inside tag values. The lexer now decodes escaped quotes/backslashes when reading tag values, and Game.String() re-escapes them when emitting PGN so values round-trip correctly.

Changes:

• Lexer: replace slice-based tag value capture with a strings.Builder that decodes \" and \\.
• Game serialization: add escapeTagValue helper and use it when formatting tag pairs.
• Add a scanner test exercising an escaped quote in an [Event ...] tag, including round-trip.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
lexer.go	Decode \" and \\ escapes in readTagValue via a string builder.
game.go	Add escapeTagValue and apply it when writing tag pairs in String().
scanner_test.go	New TestEscapedQuoteInTagValue verifying parse and round-trip behavior.

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