Fix attribute parsing edge cases for curly braces, colons, and escapes

[dereuromark]

Summary

This PR fixes three issues in attribute parsing to match the reference JS implementation behavior:

1. Curly braces in quoted values

Use findAttributeEnd() instead of naive strpos() for finding attribute block boundaries. This properly handles quoted strings containing { and } characters.

Before:

Input:  [text]{code="{foo}"}
Output: <p><span>text</span>"}</p>  ← broken

After:

Input:  [text]{code="{foo}"}
Output: <p><span code="{foo}">text</span></p>  ✓

2. Colon in attribute keys

Allow colons in attribute key names to support namespaced attributes like xml:lang=en. Also made key patterns more permissive to allow underscore/hyphen prefixed keys after whitespace.

Before:

Input:  [text]{xml:lang=en}
Output: <p><span lang="en">text</span></p>  ← colon prefix stripped

After:

Input:  [text]{xml:lang=en}
Output: <p><span xml:lang="en">text</span></p>  ✓

3. Backslash escape handling

Process escapes correctly for ASCII punctuation (\\, \", \*, etc.) while keeping backslash before alphanumerics literal (\n, \t, \U stay as-is).

Before:

Input:  [text]{path="C:\Users\test"}
Output: <p><span path="C:Userstest">text</span></p>  ← backslashes removed

After:

Input:  [text]{path="C:\Users\test"}
Output: <p><span path="C:\Users\test">text</span></p>  ✓

Changes

• src/Parser/InlineParser.php: Replace strpos($text, '}', ...) with findAttributeEnd() in 4 places
• src/Parser/Utility/AttributeParser.php:
  • Update key patterns to allow colons and be more permissive
  • Fix processEscapes() to only escape ASCII punctuation
• tests/TestCase/Parser/AttributeParserTest.php: Add 17 new tests

All verified against reference JS implementation (@djot/djot).

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.64%. Comparing base (e35734f) to head (6797754).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Parser/InlineParser.php	75.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #110      +/-   ##
============================================
+ Coverage     93.61%   93.64%   +0.03%     
- Complexity     2328     2332       +4     
============================================
  Files            79       79              
  Lines          6168     6182      +14     
============================================
+ Hits           5774     5789      +15     
+ Misses          394      393       -1     

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