[BugFix] Fix missing raise, incorrect __torch_function__ return, and off-by-one in RayCollector

[jashshah999]

Summary

Fixes three independent bugs found during code review:

• collectors/_runner.py: RuntimeError(MPS_ERROR) is constructed but never raised, silently allowing execution to continue when tensors are on MPS devices instead of failing with a clear error
• data/tensor_specs.py: TensorSpec.__torch_function__ returns a NotImplementedError(...) instance instead of the NotImplemented sentinel, violating the __torch_function__ protocol and causing downstream confusion since the caller receives an exception object as a valid return value
• collectors/distributed/ray.py: update_policy_weights_() is called with collector_index + 1, but collector_index is already 0-indexed (it comes from pending_tasks.pop(future)), so the +1 causes weight updates to target the wrong worker

Changes

All three fixes are minimal:

1. Add raise before RuntimeError(MPS_ERROR) in _runner.py:490
2. Replace return NotImplementedError(...) with return NotImplemented in tensor_specs.py:1232
3. Remove + 1 from collector_index + 1 in ray.py:1013

Fixes #3000

[pytorch-bot]

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❌ 6 New Failures, 5 Pending, 21 Unrelated Failures

As of commit faa0a24 with merge base ab0a445 ():

NEW FAILURES - The following jobs have failed:

• Build Linux Wheels / pytorch/rl (pytorch/rl, test/smoke_test.py, torchrl, .github/scripts/pre-build-script.sh) / build-manywheel-py3_10-rocm7_2 (gh)
  Process completed with exit code 1.
• Generate documentation / build-docs (3.12, 12.8) / linux-job (gh)
• Lint / c-source / linux-job (gh)
  The process '/usr/bin/git' failed with exit code 128
• Lint / python-source-and-configs / linux-job (gh)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / upload-codecov (gh)
  Process completed with exit code 1.
• Unit-tests on Windows / unittests-cpu (3.10, windows.4xlarge, cpu) / windows-job (gh)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 128

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• Libs Tests on Linux / unittests-gym (3.10, 12.8) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Libs Tests on Linux / unittests-sklearn (3.10, 12.8) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• SOTA Tests on Linux / tests (3.10, 13.0) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Tutorials Tests on Linux / tests (3.12, 12.4) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / test-setup-minimal (3.10) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Unit-tests on Linux / test-setup-minimal (3.14) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Unit-tests on Linux / tests-cpu (3.10) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-cpu (3.11) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-cpu (3.12) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Unit-tests on Linux / tests-cpu (3.13) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-cpu (3.14) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-gpu (3.12, 13.0, 1) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-gpu (3.12, 13.0, 2) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-gpu (3.12, 13.0, 3) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-gpu-distributed (3.12, 13.0) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-olddeps (3.10, 11.8) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-optdeps (3.12, 13.0) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Unit-tests on Linux / tests-stable-gpu (3.12, 13.0, 1) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-stable-gpu (3.12, 13.0, 2) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-stable-gpu (3.12, 13.0, 3) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128
• Unit-tests on Linux / tests-stable-gpu-distributed (3.12, 13.0) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 128

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