Use numpydoc to render the API reference

[vlad-perevezentsev]

This PR switches the documentation build from sphinx.ext.napoleon to numpydoc to render the API reference.
numpydoc renders the Parameters and Returns sections as definition lists out of the box, which lets us remove:

• the custom doc/_static/dpnp-custom.js that reformatted parameter
  descriptions, together with the CSS rules that only supported it;
• the napoleon monkeypatch for namedtuple Returns (numpydoc handles it
  natively).

A small hook keeps the dpnp-specific Limitations section and a some docstrings are adjusted for numpydoc's stricter parser.

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[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/pull/3059/index.html

[github-actions]

Array API standard conformance tests for dpnp=0.21.0dev7=py314ha0e2e8e_18 ran successfully.
Passed: 1375
Failed: 0
Skipped: 7

[coveralls]

coverage: 78.489% (-0.003%) from 78.492% — use_numpydocs_in_docs_build into master