[python] Support `tiledbsoma.io.update_obs` with post-nullable non-string attributes

[johnkerl]

Problem:

• This comment https://github.com/single-cell-data/TileDB-SOMA/blob/1.11.4/apis/python/src/tiledbsoma/_arrow_types.py#L267-L281 is very clear about why and how customers can ingest data with no nulls in a given column, then either tiledbsoma.io.update_obs or append-mode ingest data which does have either all nulls, or a mix of null and non-null
• User-level symptom: the tiledbsoma.io.update_obs or append-mode ingest fails with Casting field 'new_col' with null values to non-nullable
  • The array had its schema created with non-nullable -- reflective of the initial input data
  • The new data has nulls, which cannot be accommodated within that schema
• The only mistake I made on that PR was restricting to string columns: https://github.com/single-cell-data/TileDB-SOMA/blob/1.11.4/apis/python/src/tiledbsoma/_arrow_types.py#L283. In fact the reasoning articulated in the above comment applies equally well to int columns, or float, or bool, etc.

Side note:

• Given that np.nan is a floating-point number -- unlike with ints/strings where Pandas allows you to stick floating-point NaN into a column containing otherwise int/string -- numpy.nan actually is a floating-point number. (This, along with Inf, is part of the IEEE floating-point specification).
• Given that we have some refactoring going on with pushing more logic down to C++, code-deduping from Python & R -- which can have minor effects
• As of tiledbsoma 1.9: I verified that if you ingested a floating-point column with NaN in it, that came in as float32 or float64 , and non-nullable
• As of tiledbsoma 1.10 and 1.11: I verified that if you attempted to ingest a floating-point column with NaN in it, that failed with Casting field 'new_col' with null values to non-nullable
• Thus it's possible that if a user had an experiment created with 1.9 or earlier which did have NaNs in a floating-point column, they would still see today Casting field 'new_col' with null values to non-nullable on an attempt to do tiledbsoma.io.update_obs with the new_col having any NaNs in it.

Marked as blocker since I want this in 1.12.0 (#2672)

[sc-49403]