Add PHP 8.4 support, PHPStan level 8 analysis, and security hardening

[parsilver]

Summary

• Add PHP 8.4 to CI test matrix
• Add PHPStan level 8 static analysis with composer analyse command
• Add Laravel Pint code formatting with strict_types enforcement
• Add security hardening: CRLF injection prevention and sensitive header redaction
• Fix PHPStan violations across the codebase

Test plan

• Run composer check (PHPStan + tests)
• Verify CI passes on all PHP versions (8.1, 8.2, 8.3, 8.4)
• Verify code formatting with composer format

[codecov]

Codecov Report

❌ Patch coverage is 88.11881% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.71%. Comparing base (19a1014) to head (aa63045).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Serialization/JsonSerializer.php	59.25%	11 Missing ⚠️
src/Factory/ClientFactory.php	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #29      +/-   ##
============================================
- Coverage     96.41%   95.71%   -0.70%     
- Complexity      426      450      +24     
============================================
  Files            33       33              
  Lines          1255     1308      +53     
============================================
+ Hits           1210     1252      +42     
- Misses           45       56      +11     

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