Add utility helper classes and tests

[ohmyfelix]

Summary

• add six new utility classes: Caster, Emptiness, System, TextString, UserAgents, and Uuid
• add phpt coverage for all new helpers, including casting exceptions, timer lifecycle, user-agent rotation/random behavior, and UUID v4 validation
• document the new helpers in .docs/README.md so they are discoverable in package docs

Testing

• make qa
• vendor/bin/tester -s -p php --colors 1 tests/Cases/Caster.phpt tests/Cases/Emptiness.phpt tests/Cases/System.phpt tests/Cases/TextString.phpt tests/Cases/UserAgents.phpt tests/Cases/Uuid.phpt
• make tests (fails in this environment because GD extension is not loaded in existing tests/Cases/File.phpt)

[codecov]

Codecov Report

❌ Patch coverage is 97.87234% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@bde9825). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/Caster.php	96.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #41   +/-   ##
=========================================
  Coverage          ?   88.93%           
=========================================
  Files             ?       26           
  Lines             ?      497           
  Branches          ?        0           
=========================================
  Hits              ?      442           
  Misses            ?       55           
  Partials          ?        0           

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