Fix stale LB25 state causing spurious breaks after colon-separated text

[JimBobSquarePants]

Prerequisites

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• I have provided test coverage for my change (where applicable)

Description

This pull request significantly improves the maintainability and clarity of the LineBreakEnumerator implementation in src/SixLabors.Fonts/Unicode/LineBreakEnumerator.cs by adding detailed, specification-driven comments, refactoring for readability, and enhancing documentation. Additionally, it introduces a new unit test to cover a previously reported issue.

Documentation and Maintainability Improvements:

• Added comprehensive XML documentation and inline comments throughout LineBreakEnumerator to closely align with the Unicode Line Breaking Algorithm (UAX 14), making rule references explicit and clarifying the purpose of internal state and logic. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

Correctness and Algorithmic Clarifications:

• Refactored and clarified handling of specific Unicode line break rules (e.g., LB8a, LB22, LB24, LB25, LB30, LB30b, LB31) to ensure correct state tracking and to make the interaction between pair-table logic and stateful exceptions more transparent. [1] [2] [3] [4] [5] [6] [7] [8]

Testing:

• Added a new test (Issues_522) to verify that the line break enumerator does not break within an alphanumeric run following a colon, addressing a previously reported issue and improving test coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82%. Comparing base (7396060) to head (75f3567).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #523   +/-   ##
=====================================
- Coverage     82%     82%   -1%     
=====================================
  Files        305     305           
  Lines      21534   21540    +6     
  Branches    3165    3167    +2     
=====================================
+ Hits       17818   17822    +4     
- Misses      2901    2903    +2     
  Partials     815     815           

Flag	Coverage Δ
unittests	82% <100%> (-1%)	⬇️

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