[Feature] Added MCTSPolicyBase, MCTSPolicy, AlphaGoPolicy, AlphaStarPolicy, and MuZeroPolicy

[ParamThakkar123]

Description

Describe your changes in detail.

Added MCTSPolicyBase, MCTSPolicy, AlphaGoPolicy, AlphaStarPolicy, and MuZeroPolicy to mcts policies.

Motivation and Context

Why is this change required? What problem does it solve?
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

This issue doesn't close but is a subtask of #2357

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

What types of changes does your code introduce? Remove all that do not apply:

• Bug fix (non-breaking change which fixes an issue)
• 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

Go over all the following points, and put an x in all the boxes that apply.
If you are unsure about any of these, don't hesitate to ask. We are here to help!

• I have read the CONTRIBUTION guide (required)
• My change requires a change to the documentation.
• 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/3449

• 📄 Preview Python docs built from this PR

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

❌ 2 New Failures, 1 Cancelled Job

As of commit 0252382 with merge base 838410c ():

NEW FAILURES - The following jobs have failed:

• Continuous Benchmark (PR) / CPU Pytest benchmark (gh)
  Workflow failed! Resource not accessible by integration
• Lint / python-source-and-configs / linux-job (gh)
  torchrl/data/tensor_specs.py:6870:1: F811 redefinition of unused '_index_select_spec' from line 6825

CANCELLED JOB - The following job was cancelled. Please retry:

• Continuous Benchmark (PR) / GPU Pytest benchmark (gh)
  Workflow failed! Resource not accessible by integration

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[github-actions]

⚠️ PR Title Label Error

PR title must start with a label prefix in brackets (e.g., [BugFix]).

Current title: Added MCTSPolicyBase, MCTSPolicy, AlphaGoPolicy, AlphaStarPolicy, and MuZeroPolicy

Supported Prefixes (case-sensitive)

Your PR title must start with exactly one of these prefixes:

Prefix	Label Applied	Example
[BugFix]	BugFix	[BugFix] Fix memory leak in collector
[Feature]	Feature	[Feature] Add new optimizer
[Doc] or [Docs]	Documentation	[Doc] Update installation guide
[Refactor]	Refactoring	[Refactor] Clean up module imports
[CI]	CI	[CI] Fix workflow permissions
[Test] or [Tests]	Tests	[Tests] Add unit tests for buffer
[Environment] or [Environments]	Environments	[Environments] Add Gymnasium support
[Data]	Data	[Data] Fix replay buffer sampling
[Performance] or [Perf]	Performance	[Performance] Optimize tensor ops
[BC-Breaking]	bc breaking	[BC-Breaking] Remove deprecated API
[Deprecation]	Deprecation	[Deprecation] Mark old function

Note: Common variations like singular/plural are supported (e.g., [Doc] or [Docs]).

[ParamThakkar123]

1 test is currently failing. Working on fixing that

[ParamThakkar123]

All tests passed locally