docs: Fix reStructuredText markup in Python docstrings

[wenzeslaus]

This fixes markup issues in the Python docstrings consumed by Sphinx. Follow-up to #7526.

Details

The Sphinx build of the Python API documentation reports docutils warnings and errors for docstrings with invalid reStructuredText, and the affected docstrings also render badly.

• grass.pydispatch.dispatcher: mark the two attribute listings as
  literal blocks, so that their plain-text layout is preserved instead
  of being misparsed as definition lists and block quotes.
• grass.pygrass.raster.abstract: drop the literal block marker in front
  of the doctest example of Info, so that the example is parsed as a
  doctest block. The expected output lines are not prefixed with ">>>",
  which made the quoting of the literal block inconsistent.
• grass.pygrass.vector.geometry: turn the parameter descriptions of the
  Node constructor into an actual field list.
• grass.gunittest.runner, grass.pygrass.vector.geometry,
  grass.tools.session_tools: escape or quote the asterisks so that
  "**kwargs" is not parsed as the start of inline strong markup.
• grass.imaging.images2avi: indent the continuation line of the bg_task
  field body, so that the field list is not cut short.
• grass.temporal.core: indent the content of the warning directive in
  init(), so that the directive is not empty.

This brings the number of warnings and errors reported by the Sphinx
build down from 42 to 19. Each fixed docstring is reported twice because
the subpackages are currently documented under two names.

The fixes were prepared with the help of Claude Code (AI) and verified
against the rendered HTML pages.