Extract Behavior CRUD out of the crud/__init__.py monolith

[akwasigroch]

Purpose

crud/__init__.py is a 1946-line monolith that the codebase is splitting one entity at a time, following #2411, #2412, #2438, #2439, #2441, #2442, #2449, #2450 and #2451. This takes the Behavior block out. Per apps/backend/AGENTS.md the package only shrinks from here — nothing new goes back into __init__.py.

What Changed

• Moved get_behavior, get_behaviors, get_behaviors_detail, create_behavior, update_behavior and delete_behavior into a new crud/behavior.py (141 lines). _BEHAVIOR_RELATED_FIELDS moved with them; nothing else in __init__.py used it.
• crud/__init__.py drops 118 lines.
• Nothing is re-exported, matching the earlier splits. All 13 call sites now use from rhesis.backend.app.crud import behavior as behavior_crud.
• Nothing dropped — all six functions have live callers.
• get_behavior had a redundant function-local QueryBuilder import; it is now module-level, matching crud/source.py. _check_and_raise_if_deleted stays local, also matching source.py.
• The module docstring records why get_behaviors_detail exists: get_behaviors is a plain get_items with no eager loading, so the list endpoint calls the detail variant instead. That variant runs two queries — IDs first with filter/sort/limit, then an eager load scoped to those IDs — and re-applies the sort in Python because WHERE id IN (...) does not preserve order. Dropping that re-sort returns the right page in the wrong order with no error.

Additional Context

• One of four parallel extractions: Behavior, File (Extract File CRUD out of the crud/__init__.py monolith #2456), Model (Extract Model CRUD out of the crud/__init__.py monolith #2457) and User (Extract User CRUD out of the crud/__init__.py monolith #2458). The four blocks were chosen so they do not touch each other in crud/__init__.py, and git merge-tree confirms __init__.py merges clean across all six pairings.
• This branch conflicts with the Model PR in services/test_config_generator.py and services/test_generation_pipeline.py. Both are the same trivial shape — each branch inserts its own crud submodule import at the same spot, so the resolution is to keep both lines. Once both land, the last bare crud. use disappears from each file and the from rhesis.backend.app import crud import must be dropped (ruff F401).
• Suggested landing order across the four: this one and File first (conflict-free), then Model, then User.
• Deliberately avoids get_test_sets and get_tests, which Add metric tuning for custom metrics [feature branch] #2446 modifies.
• Does not act on Add implementation plan for Behaviors to Requirements rename #2199 (the Behaviors → Requirements rename proposal); this is a pure move.

Testing

Pure move — behaviour is unchanged, so the existing suite is the check.

cd apps/backend
uv run pytest ../../tests/backend/routes/test_behavior.py ../../tests/backend/utils/test_query_builder_load.py ../../tests/backend/services/test_test_generation_pipeline.py ../../tests/backend/crud/
# 166 passed, 2 skipped, 1 xfailed

uv run pytest ../../tests/backend/services ../../tests/backend/utils ../../tests/backend/security ../../tests/backend/auth
# 3518 passed, 4 skipped, 1 xfailed

Ruff clean on all 7 touched files. A repo-wide grep for crud.get_behavior, crud.get_behaviors, crud.get_behaviors_detail, crud.create_behavior, crud.update_behavior and crud.delete_behavior returns nothing.

Worth a reviewer's eye: tests/backend/services/test_test_generation_pipeline.py patched the module-level name ...test_generation_pipeline.crud and set crud.get_behaviors.return_value. After the move that patch still applies cleanly but stubs nothing, so the tests would have reached a real DB call through a MagicMock session and passed for the wrong reason. Retargeted to behavior_crud.

[peqy]

Looks good. Clean extraction into crud/behavior.py and the call sites/tests were updated correctly (especially the patch() retargeting). Ship it.