Enable the D417 Ruff rule and stop repeating type annotations in docstrings

[mmacferrin]

Progress on #40. Two commits, each independently green.

1. Enable D417 and set the Google docstring convention

D417 (undocumented-param) was suppressed because it reported nine functions with undocumented parameters. Eight of those were false positives. No pydocstyle convention was configured, so Ruff parsed the Parameters + dashed-underline headers as NumPy sections, found no NumPy-formatted entries inside, and reported every argument as undocumented.

The docstring bodies are Google-style throughout, and docs/source/conf.py already sets napoleon_google_docstring = True, so the convention is pinned to google. That takes D417 from 9 findings to 1; numpy would have left 8. The only rules the convention retires are D400, whose check is subsumed by the still-active D415, and the cosmetic D413.

The 49 dashed section headers become Args:/Returns:/Raises:, and the parameters that were genuinely undocumented — visible only once the sections parsed — are filled in: omit_bboxes, gdf, auto_clean_csv, tolerance, three in process_parallel, and dem_ndv / min_confidence_level / min_bathy_confidence in validate_dem, worded from the CLI help for the matching options.

D417 also caught a real documentation bug: process_parallel documented a kwargs_lists parameter that the signature spells kwargs_list.

Ignore list: 57 → 56.

2. Let annotations be the only source of parameter types

Google's style guide asks for a type in an Args: entry only when the signature does not annotate the parameter, and conf.py loads sphinx_autodoc_typehints with always_document_param_types = True — so an annotated parameter already renders its type and default from the signature. A hand-written type is a duplicate that can contradict it, and did:

	count
params documented with a type	86
annotated and agreeing	45
annotated and divergent	28
unannotated (docstring is the only source)	13

The drift was almost entirely a | None added to a signature and never to the prose — validate_dem's output_dir claimed str against an annotation of str | None. The type is dropped from all 73 annotated parameters and kept, in Google name (type): form, for the 13 without annotations.

Three problems in the same docstrings were stopping Sphinx from rendering these sections at all, and are fixed here too:

• 30 entries were NumPy-shaped (name : type, prose on the next line). Napoleon splits on the first colon, so the type rendered as the opening words of the description.
• 22 section bodies sat flush with their header instead of indented under it. D417 accepts that; napoleon reads the section as empty and emits no parameters.
• 3 Raises: blocks put the exception name on its own line.

Verification

Running every docstring through napoleon with this repo's own conf.py settings, counting parameters emitted as real :param: fields in the files touched here:

	:param fields
main	50
this branch	124

No documented parameter fails to render, and no rendered description still opens with a bare type.

ruff check, ruff format and the full prek suite pass at both commits. No code changed anywhere — every edited file was verified to produce an identical AST once docstring constants are blanked, with docstring counts unchanged.

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🔍 Docs preview: https://ivert--104.org.readthedocs.build/en/104/