[Algorithm] Discrete IQL

[BY571]

Description

Adding discrete IQL Loss + example script.

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Motivation and Context

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If it fixes an open issue, please link to the issue here.
You can use the syntax close #15213 if this solves the issue #15213

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Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• [X ] New feature (non-breaking change which adds core functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of examples)

Checklist

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• I have read the CONTRIBUTION guide (required)
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• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/rl/1793

• 📄 Preview Python docs built from this PR

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✅ You can merge normally! (6 Unrelated Failures)

As of commit 65746f2 with merge base 5b3dd98 ():

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

• 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
• Examples Tests on Linux / tests (3.9, 12.1) / linux-job (gh)
  RuntimeError: Command docker exec -t 72cebda70c148d10617e9343ae20b744caea1ce419f432a1b0749813385eeba1 /exec failed with exit code 245
• Unit-tests on Linux / tests-stable-gpu (3.8, 11.8) / linux-job (gh)
  test/test_rb.py::TestStorages::test_storage_state_dict[torchsnapshot-False-memmap-memmap]

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

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

• Habitat Tests on Linux / tests (3.9, 11.6) / linux-job (gh)
  test/test_libs.py::TestHabitat::test_habitat_render[False-HabitatPick-v0]
• Unit-tests on Windows / unittests-gpu / windows-job (gh)
  ##[error]The operation was canceled.

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[BY571]

Performance tested on CartPole:

[vmoens]

LGTM just some very minor changes to make! Thanks a million

[vmoens]

@BY571 we have a device exception that is being triggered

https://github.com/pytorch/rl/actions/runs/7530079022/job/20495721891?pr=1793

Do you know why?

[vmoens]

LGTM thanks for this