[Feature] timeit.mark_start/mark_end for non-context-manager timing

[vmoens]

Stack from ghstack (oldest at bottom):

• [Feature] Collector.fake_tensordict() / MultiCollector.fake_tensordict() #3761
• [Example] Isaac Lab RNN PPO with compact memory + knowledge-base notes #3760
• [Feature] MultiCollector: track policy version per fresh continue command #3759
• [Feature] Collector final_obs: store true boundary next-obs for shifted-GAE #3758
• [BugFix] GAE shifted=True: tolerate missing next obs, non-canonical strides, docs #3757
• -> [Feature] timeit.mark_start/mark_end for non-context-manager timing #3756
• [BugFix] PolicyVersion: int64 dtype + preserve tensordict device #3755
• [Performance] LSTM/GRU scan: canonical strides + cuDNN flat-storage clones + thread-local recurrent mode #3754
• [BugFix] Recurrent policy auto-register with policy_factory #3753

The collector worker loop needs to time spans that begin in one branch
of a control-flow path and end in another — picking up the next
continue command, then ending after the env step. with timeit(...)
can't bridge that.

Refactor __exit__ through a new _record(name, elapsed) classmethod
so the recording side is callable independently. Add timeit.mark_start
/ timeit.mark_end (and mark_env alias) on top: they push and pop
into a class-level _MARKS dict and feed _record on end. The
context-manager path is unchanged.

Unit tests cover: round-trip into _REG, mark cleanup on end, alias
identity for mark_env, and that with timeit(...) still records.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/rl/3756

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• Run pull request jobs on OSDC runners in shadow mode

❌ 4 New Failures, 14 Pending

As of commit 457d247 with merge base 0a01ee8 ():

NEW FAILURES - The following jobs have failed:

• Continuous Benchmark (PR) / CPU Pytest benchmark (gh)
  Process completed with exit code 1.
• Continuous Benchmark (PR) / GPU Pytest benchmark (gh)
  Process completed with exit code 1.
• Lint / lint-done (gh)
  Process completed with exit code 1.
• Lint / python-source-and-configs / linux-job (gh)
  RuntimeError: Command docker exec -t f48dc3c9322eb1afc551a1d3f8e443e31edbeafa2c9e97e4e6eaf95d8ec27789 /exec failed with exit code 1

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[vmoens]

remove this