refactor(mettagrid): remove clipper system

[daveey]

refactor(mettagrid): remove clipper system

Remove the clipper system entirely from mettagrid and cogames.
This is preparation for replacing it with a more general events system.

Changes:

• Remove Clipper class and ClipperConfig from C++ codebase
• Remove clipper from Python config classes
• Remove clip_period, start_clipped, clip_immune fields from assemblers
• Remove clipping-related missions (RepairMission, HelloWorldUnclipMission)
• Remove clipping-related variants (ClipHubStationsVariant, ClipPeriodOnVariant, etc.)
• Remove unclipping diagnostic evals
• Update tests to remove clipping assertions

Note: Scripted agents that reference clipping will need separate cleanup.

Co-Authored-By: Claude Opus 4.5 noreply@anthropic.com

refactor(nim): remove clipping references from Nim agents

Remove clipped field from ObservedObject and ExtractorInfo types,
remove clipped feature parsing from common.nim, and remove unclipping
evals from thinky_eval.py.

Co-Authored-By: Claude Opus 4.5 noreply@anthropic.com

[daveey]

• feat(mettagrid): add StatsMutation for logging stats #4958 : 2 dependent PRs (#4959 , #4960 )
• feat(mettagrid): add AlignToCollectiveMutation for direct collective alignment #4957
• feat(mettagrid): add CollectiveFilter for filtering by collective membership #4956
• feat(mettagrid): add ObjectTypeFilter for filtering by object type #4955
• feat(mettagrid): add events system core infrastructure #4954
• refactor(mettagrid): remove clipper system #4953 👈 (View in Graphite)
• main

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[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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[openhands-ai]

Looks like there are a few issues preventing this PR from being merged!

• GitHub Actions are failing:
  • Test and Benchmark

If you'd like me to help, just leave a comment, like

@OpenHands please fix the failing actions on PR #4953 at branch `01-16-refactor_mettagrid_remove_clipper_system`

Feel free to include any additional details that might help me get this PR into a better state.

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