feat(repository): add stream() for memory-bounded iteration over large collections

[guillaumedelre]

Ref: #144

Introduces stream() on AbstractObjectRepository and RedisObjectManager, yielding objects in configurable batches without loading the full collection into memory.

• RepositoryInterface: add stream(criteria, orderBy, batchSize) signature
• AbstractObjectRepository: implement stream(); findAll() delegates to it
• RedisObjectManagerInterface/RedisObjectManager: add stream() with automatic identity map clearing between batches
• Tests: functional coverage for Hash and Json formats (criteria, orderBy, empty collection, small batchSize, exact batch multiple, manager variant with identity map verification)
• docs/advanced_usage.md: document both forms and their constraints
• README.md: add Unique Constraints and Streaming sections, update feature list
• style: apply php-cs-fixer to pre-existing violations in tests/

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.47%. Comparing base (3dbfb4c) to head (1cef385).
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Additional details and impacted files

@@             Coverage Diff              @@
##               main     #145      +/-   ##
============================================
+ Coverage     87.43%   87.47%   +0.03%     
- Complexity      949      951       +2     
============================================
  Files            70       70              
  Lines          2221     2228       +7     
============================================
+ Hits           1942     1949       +7     
  Misses          279      279              

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