Fix continuation indentation in Google return descriptions

[Michael-WhiteCapData]

Dedent continuation text after the type and description in Google style Returns sections. Previously, a wrapped description rendered as a definition list instead of a paragraph, with or without inline markup.

Preserves indentation after a blank line so literal blocks retain their existing formatting. Adds cases for plain text, interpreted text, and inline literals.

Fixes #13602.

Validation: all 72 Napoleon tests pass, including the existing return code block test. Targeted mypy, Ruff checks, and formatting pass. The push hook also passed all 20 JavaScript browser specs.

[Michael-WhiteCapData]

CI follow-up: the standard Python jobs and static checks pass. The Docutils HEAD job reports HTML parsing failures; I reproduced the same mismatched tag: line 139, column 2 on unchanged upstream b04a2101295ac3fb725b16111eda0284b6da4cca with Docutils 35b59ca7d0645e6d7c5581a34b75f6a0feb799cc. The baseline markup subset has 64 failures and 4 passes. The LaTeX job also installs that Docutils development revision and reports the same HTML failure among additional failures.

The Python 3.13t and 3.14t jobs fail in the unchanged test_cfunction expectation: time.asctime reports time_tuple, while the test expects tuple. My available Windows 3.13.15t baseline passes that test, so this is not a claim to have reproduced the hosted 3.13.16 environment locally. I have not exhaustively reproduced every LaTeX job failure.

Additional baseline verification: on unchanged upstream b04a210, Python 3.14.7 on Windows with development Docutils reproduces four representative failures: test_footnote_referred_multiple_times (LaTeX), test_texinfo, test_lineblock, and test_highlight_language_default (doctest). With Docutils 0.22.3, the same selection gives 3 passed and 1 skipped (Texinfo requires an unavailable external tool). This extends the baseline evidence without claiming that every hosted LaTeX failure has been reproduced.