Standardize docstrings in metrics module to Google-style format

[yukthagangadhari5]

Describe your changes

This PR standardizes the docstrings in neural_lam/metrics.py to a
consistent Google-style format.

The goal is to improve documentation clarity and ensure compatibility
with Sphinx + napoleon for automated API generation.

Changes are documentation-only and do not modify any functionality.
No behavioral changes introduced.

Issue Link

Related to #61 (structured documentation improvements)

Type of change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📖 Documentation

Checklist before requesting a review

• My branch is up-to-date with the target branch
• I have performed a self-review of my code
• For modified functions I have added standardized docstrings
• I have updated the README (not applicable)
• I have added tests (not applicable — documentation-only change)

[sadamov]

this is a duplicate of #252 , please add your contribution there

[yukthagangadhari5]

Thanks for the clarification.

I wasn’t aware that similar changes were already being tracked in #252.
Happy to contribute the docstring updates there instead.

Please let me know if you'd prefer a specific approach for integrating them.