Improve code documentation

[dereuromark]

Summary

• Added comprehensive class-level PHPDoc to Scheduler class
• Added detailed method documentation with parameter descriptions

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.88%. Comparing base (9e30d7e) to head (a93bdcd).
⚠️ Report is 3 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff            @@
##             master      #15   +/-   ##
=========================================
  Coverage     76.88%   76.88%           
  Complexity      144      144           
=========================================
  Files            11       11           
  Lines           411      411           
=========================================
  Hits            316      316           
  Misses           95       95           

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