[mujoco] Add native MyoSuite EnvPool integration

[Trinkle23897]

Description

Adds a native C++ EnvPool integration for the pinned MyoSuite v2.11.6 surface under the MuJoCo family. The runtime loads generated upstream metadata and assets from third_party/myosuite/ and registers the full official ID set plus EnvPool aliases without importing the official Python package at runtime.

Key review points:

• Native runtime entrypoint and task implementation live in envpool/mujoco/myosuite/.
• Upstream source, SimHive asset wiring, generated registry metadata, pinned oracle requirements, and the MuJoCo 3.6 MjSpec compatibility patch live under third_party/myosuite/.
• Official MyoSuite is used only by tests and doc-generation tooling as a pinned oracle.
• Nine upstream IDs that fail official oracle instantiation in this pinned NumPy 2 test environment are excluded only from oracle tests; they remain registered and covered by EnvPool registry/determinism tests.
• Documentation includes the MyoSuite environment page and the generated EnvPool-vs-official render comparison image.

Motivation and Context

MyoSuite exposes a large MuJoCo task surface that was not available through EnvPool. This adds a packaged native implementation so users can create MyoBase/Reorient, Walk/Terrain, MyoChallenge, and MyoDM-style registered IDs through EnvPool without a Python runtime bridge.

• 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? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds core functionality)
• New environment (non-breaking change which adds 3rd-party environment)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of example)

Implemented Tasks

• Register the full pinned MyoSuite ID surface and EnvPool aliases.
• Add native MuJoCo-backed MyoSuite runtime, metadata/assets, tests, and docs.
• Add oracle, determinism, registry, render, docs, and release-wheel validation coverage.

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.
• I have reformatted the code using make format (required)
• I have checked the code using make lint (required)
• I have ensured make bazel-test pass. (required)

Validation run:

• make ruff py-format cpplint clang-format buildifier
• make mypy
• bazel test --config=test --cache_test_results=no --test_output=errors //envpool/mujoco:myosuite_test //envpool/mujoco:myosuite_oracle_align_test //envpool/mujoco:myosuite_render_test
• make BAZEL_TEST_TARGETS='//envpool/mujoco:mujoco_render_test //envpool/mujoco:mujoco_dmc_render_test //envpool/mujoco:robotics_test' bazel-test
• make BAZEL_TEST_TARGETS='//envpool:make_test' bazel-test
• make bazel-test (62/62 tests passed locally)
• make -C docs html (succeeds; 4 existing cpp_interface.rst Breathe warnings remain)
• make bazel-release
• make pypi-wheel
• installed the generated wheel in a fresh venv and ran make release-test
• git diff --cached --check

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