Consolidate locking dependencies into LockContext

[benrowe]

Summary

• Created new LockContext class to bundle all locking dependencies
• Updated StateFlow constructor to accept single nullable LockContext instead of three separate nullable parameters
• Updated all test files to use new LockContext API

Benefits

• ✅ Single nullable dependency for locking
• ✅ Impossible to provide partial locking configuration
• ✅ Cleaner API for users
• ✅ All locking concerns in one place
• ✅ Easier to test (one mock vs three)

Breaking Change

This is a breaking change to StateFlow constructor signature. Since project is alpha, no migration path needed.

Closes #25

Test plan

• All existing tests pass (367 tests, 1244 assertions)
• 100% code coverage maintained
• All quality checks pass (lint, PHPStan, PHPMD)
• New unit tests for LockContext class

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