Improved docs for module.py + multiple cleanups in docs

[CharlelieLrt]

PhysicsNeMo Pull Request

Description

Closes #1177 #1178 #1176 #1169 .

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• The CHANGELOG.md is up to date with these changes.
• An issue is linked to this pull request.
• If I am implementing a new model or modifying any existing model, I have followed the Models Implementation Coding Standards.

Dependencies

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[greptile-apps]

Greptile Summary

This PR significantly rewrites the docs/api/models/modules.rst reference page and adds doctest examples to physicsnemo/utils/checkpoint.py. The documentation improvements are substantial and well-structured, with proper cross-references, new sections (Backward Compatibility, dedicated API Reference), corrected import paths (physicsnemo.core.meta instead of physicsnemo.models.meta), and removal of stale content (e.g., the deprecated StaticCaptureTraining section).

Key changes:

• modules.rst: Comprehensive rewrite with :class:, :meth:, :func:, and :ref: cross-references; new Backward Compatibility and ModelRegistry sections; timm third-party integration example; corrected entry-point format ("mypackage.models:MyPhysicsNeMoModel") and Module.from_torch instead of removed Module.from_pytorch.
• checkpoint.py: Adds doctest examples to save_checkpoint and load_checkpoint.
• Issue found: The "Load a specific epoch" doctest in load_checkpoint is misleading. save_checkpoint with epoch=0 never stores the epoch in the .pt training-state file (the if epoch: guard is False for 0), so no .pt file is created for epoch 0. load_checkpoint then returns 0 as a default fallback — not from an actual checkpoint — making the example appear to work correctly while hiding the underlying behaviour.

Important Files Changed

Filename	Overview
docs/api/models/modules.rst	Major documentation rewrite for the PhysicsNeMo modules page: adds cross-references using :class:/:meth:/:func: roles, new sections for Backward Compatibility and a dedicated API Reference, removes stale StaticCaptureTraining content, and adds timm integration and model registry usage examples. All code snippets were verified against the actual implementation.
physicsnemo/utils/checkpoint.py	Adds doctest examples to save_checkpoint and load_checkpoint. The first save/load example is correct. The "Save multiple models" example is correct. The "Load a specific epoch" example is misleading: save_checkpoint with epoch=0 never writes the epoch into the .pt file (due to if epoch: being falsy for 0), so load_checkpoint returns 0 as a default fallback rather than from the checkpoint, masking a subtle pre-existing behaviour.

_{Last reviewed commit: 5f5ddb5}