Streamline docstrings and fix documentation rendering bugs

[azrael417]

Problem

Docstring conventions had drifted across the package, and a few inconsistencies were actually breaking autodoc output. Since the docs have not been published yet, this is a good time to
normalize them.

Changes

Rendering bugs (visible in the built HTML)

• examples/losses.py: two docstrings (incl. the public forward on the loss base class) were Google-style, but conf.py sets napoleon_google_docstring = False — they rendered as literal prose
  with no parameter table. Converted to NumPy style.
• examples/models/sfno.py: Example: with a trailing colon isn't recognized by napoleon, so the header and its underline leaked into the page as raw text.
• 10 API pages published PyTorch's boilerplate ("Define the computation performed at every call") because forward/to lack docstrings and autodoc inherits from nn.Module. Fixed with
  autodoc_inherit_docstrings = False.

Consistency (no rendering change)

• 237 × name: type → name : type; 63 underline lengths corrected; 6 × Example → Examples.
• Returns unified: single-value → bare type, multi-value → named entries (numpydoc convention).

Docs config

• nitpicky = True with a small nitpick_ignore; with CI's existing -W, a broken cross-reference now fails the build instead of accumulating silently.
• Added matplotlib to intersphinx_mapping; excluded jupyter_execute (myst-nb copies were rediscovered as source on rebuild).
• Qualified one :class: reference in distributed_attention.py.

Testing

Full Sphinx build against the working tree: 0 warnings (down from 104 in nitpicky mode). Verified nitpicky is genuinely active by injecting a bogus reference — caught with the new config,
silent under -D nitpicky=0.

Rendered-output diff through napoleon is exactly 12 lines, all intended Returns changes — confirming the 237 colon and 63 underline edits are render-neutral. AST comparison with docstrings
stripped shows 0 non-docstring differences across all 27 files.

API / numerical behavior

None. Docstrings, docs/conf.py, and one cross-reference only; no code paths touched.

[albertocarpentieri]

Can we add build/ and *.egg-info to the .gitignore?

[albertocarpentieri]

All good, mostly docs and formatting