refactor: extract CommandExecutionContext to decouple BrowserManagerHandle from TaskManager

[vringar]

Summary

• Extract FailureTracker class from TaskManager's inline failure tracking fields
• Define CommandExecutionContext protocol that BrowserManagerHandle depends on instead of TaskManager directly
• Update BrowserManagerHandle to use the protocol, breaking the circular dependency
• TaskManager implements the protocol via store_record() and finalize_visit_id() methods

This enables mock-based unit testing of BrowserManagerHandle without needing a full TaskManager.

Stacked on #1124.

[codecov]

Codecov Report

❌ Patch coverage is 63.88889% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.03%. Comparing base (8d36d7f) to head (1be210b).

Files with missing lines	Patch %	Lines
openwpm/browser_manager.py	21.42%	11 Missing ⚠️
openwpm/failure_tracker.py	72.72%	9 Missing ⚠️
openwpm/task_manager.py	71.42%	4 Missing ⚠️
openwpm/command_execution_context.py	81.81%	2 Missing ⚠️

Additional details and impacted files

@@                      Coverage Diff                       @@
##           refactor/architecture-docs    #1125      +/-   ##
==============================================================
+ Coverage                       36.17%   44.03%   +7.86%     
==============================================================
  Files                              35       37       +2     
  Lines                            3475     3522      +47     
==============================================================
+ Hits                             1257     1551     +294     
+ Misses                           2218     1971     -247     

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