Remove stdClass support, enable pure entity trees

[alganet]

Drop stdClass entities: all hydration now produces typed classes. Simplify extractColumns to a one-liner delegating to EntityFactory::extractColumns() + filterColumns(). Simplify getRelatedEntity keeping the FK-field fallback for backward compatibility with OtherEntity-style setters.

Entity stubs use pure entity trees: relation properties ($post, $author) replace FK scalars. OtherEntity\Post marks its derived $author as #[NotPersistable] since it keeps explicit $author_id.

Remove 5 redundant tests (identical duplicate + fetch/fetchAll pairs). Add coverage for LEFT JOIN null-child, non-existent row fetch, pure entity tree FK derivation on persist.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.32%. Comparing base (325dea6) to head (e86946f).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #108      +/-   ##
============================================
- Coverage     98.83%   98.32%   -0.51%     
+ Complexity      178      172       -6     
============================================
  Files             4        4              
  Lines           430      419      -11     
============================================
- Hits            425      412      -13     
- Misses            5        7       +2     

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[Copilot]

Pull request overview

This PR removes stdClass-based entity hydration in favor of always producing typed entities, and updates tests/stubs to reflect “pure entity tree” relationships (relation properties instead of FK scalars).

Changes:

• Replace Mapper::extractColumns() custom extraction logic with delegation to EntityFactory::extractColumns() plus existing column filtering.
• Update test stubs and mapper tests to use typed entities (and relation properties like $post->author, $comment->post) rather than stdClass / FK scalar fields.
• Adjust and streamline tests, adding coverage for non-existent row fetch and join-related edge cases.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Mapper.php	Simplifies column extraction by delegating to EntityFactory::extractColumns() and keeping existing filtering.
tests/MapperTest.php	Refactors tests to assert on typed entities and relation properties; adds new edge-case tests and removes redundant ones.
tests/Hydrators/FlatNumTest.php	Updates typed hydration test to resolve to Bug instead of stdClass and uses a namespaced EntityFactory.
tests/Stubs/Post.php	Shifts Post to relation-based shape (e.g., $author) consistent with pure entity trees.
tests/Stubs/Comment.php	Uses relation property $post instead of FK scalar + duplicate relation field.
tests/Stubs/OtherEntity/Post.php	Marks derived $author as #[NotPersistable] for backward-compatible setter behavior.
tests/Stubs/Author.php	Adds typed entity stub used by hydration/persist tests.
tests/Stubs/Category.php	Adds typed entity stub used by hydration/persist tests.
tests/Stubs/PostCategory.php	Adds typed entity stub for join-table scenarios.
tests/Stubs/Issue.php	Adds typed stub for singular issue table scenarios.
tests/Stubs/Issues.php	Adds typed stub for plural issues table scenarios.

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