fix(dataset): stop split mutation, determinize VOC, guard collisions

[Borda]

• train_test_split seeded the global random module and shuffled the caller's list in place, so DetectionDataset.split() reordered its own image_paths and polluted process-wide randomness; use a local random.Random and shuffle a copy
• Pascal VOC class ids were assigned in set-iteration and filesystem-glob order, so the same dataset produced different class_id values across runs; sort class names and the loaded file list
• dataset exports keyed output files on basename, silently overwriting when two entries shared a name across directories (common after merge()); detect basename collisions and raise
• add regression tests for split determinism, VOC id stability, and export collisions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85%. Comparing base (15dbbb5) to head (0495539).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2394   +/-   ##
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  Coverage       85%     85%           
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  Files           70      70           
  Lines        10013   10035   +22     
=======================================
+ Hits          8467    8489   +22     
  Misses        1546    1546           

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[Copilot]

Pull request overview

This PR improves dataset utility determinism and safety across DetectionDataset splitting/loading/exporting by eliminating global RNG side effects, making Pascal VOC class-id assignment stable, and preventing silent overwrites during flat-directory exports.

Changes:

• Make train_test_split() RNG-isolated (no global random seeding) and avoid mutating the caller’s input list.
• Determinize Pascal VOC loading by sorting discovered image files and sorting per-file discovered class names before extending the class list.
• Add export-time guards to detect basename/stem collisions before writing images/labels/XML, plus regression tests covering all three behaviors.

Quality assessment (1–5):

• Code quality: 4/5
• Tests: 5/5
• Docs: 4/5

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/supervision/dataset/utils.py	Adds collision guard helper and makes train_test_split() deterministic/isolation-friendly.
src/supervision/dataset/formats/pascal_voc.py	Ensures stable image traversal order and stable class-id assignment.
src/supervision/dataset/formats/yolo.py	Prevents YOLO label overwrites by validating output-name uniqueness up front.
src/supervision/dataset/core.py	Adds collision checks for Pascal VOC export annotations.
tests/dataset/test_utils.py	Adds regression tests for split RNG isolation and collision detection helper.
tests/dataset/test_core.py	Adds regression test ensuring as_yolo() raises on colliding basenames.
tests/dataset/formats/test_pascal_voc.py	Adds regression tests validating deterministic VOC class ordering and stable class-ids across runs.