Update docstrings for new-shape feature

[johnkerl]

Issue and/or context: As tracked on issue single-cell-data/TileDB-SOMA#2407 [sc-51048].

Note that the intended Python and R API changes are all agreed on and finalized as described in single-cell-data/TileDB-SOMA#2407

Changes:

Notes for Reviewer:

[nguyenv]

Ltgm. Minor typing suggestions.

[johnkerl]

@nguyenv alas on my most recent commit I get

python-spec/src/somacore/data.py:176: error: X | Y syntax for unions requires Python 3.10  [syntax]
python-spec/src/somacore/data.py:310: error: X | Y syntax for unions requires Python 3.10  [syntax]
Found 2 errors in 1 file (checked 21 source files)