[BugFix] Fix Ray collector on Python > 3.8

[albertbou92]

Description

This PR should fix the issues with Ray and Python > 3.8

Ray uses the inspect module it its process to convert a class into a remote object to inspect the methods. If the class has methods ( in particular getitems_) that return a GenericAlias object, the inspect.signature(...) will throw an error. It is explained very well here: ray-project/ray#43117.

Therefore, I assume the long term fix should come from the inspect module.

However, since at least for our collectors the only problematic methods was indeed _getitems__, we can just declared it and not return a GenericAlias object.

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You can use the syntax close #15213 if this solves the issue #15213

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[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/rl/2015

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❌ 4 New Failures, 2 Unrelated Failures

As of commit 15766ab with merge base e3b66bb ():

NEW FAILURES - The following jobs have failed:

• Continuous Benchmark (PR) / CPU Pytest benchmark (gh)
  Workflow failed! Resource not accessible by integration
• Continuous Benchmark (PR) / GPU Pytest benchmark (gh)
  Workflow failed! Resource not accessible by integration
• Habitat Tests on Linux / tests (3.9, 11.6) / linux-job (gh)
  RuntimeError: Command docker exec -t f9742394a740f2333e535f8ed78c81ce811045016eb28e974268e67b8ebb6e75 /exec failed with exit code 139
• Unit-tests on MacOS CPU / tests (3.8) / macos-job (gh)
  AttributeError: 'OrphanPath' object has no attribute 'exists'

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Unit-tests on Linux / tests-cpu (3.8) / linux-job (gh)
  AttributeError: 'OrphanPath' object has no attribute 'exists'
• Unit-tests on MacOS CPU / tests (3.11) / macos-job (gh)
  test/test_modules.py::TestMultiAgent::test_multiagent_mlp[batch1-None-False-True-3]

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[vmoens]

Indeed this is a big fix! Thanks for this