[c++] Final update for Python/R metadata typing

[johnkerl]

Issue and/or context: For #2698

I ran an audit here: https://gist.github.com/johnkerl/a9eb64de62f881e80cd8e7ee54aa1c5c

Findings:

• Python: At initial group-creation and array-creation time we have these:
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/libtiledbsoma/src/soma/soma_group.cc#L58-L68
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/libtiledbsoma/src/soma/soma_array.cc#L65-L75
  • These explicitly, and correctly, specifies type TILEDB_STRING_UTF8
• Python: For subsequent post-create metadata updates we have this:
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/apis/python/src/tiledbsoma/_tdb_handles.py#L531-L536
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/apis/python/src/tiledbsoma/soma_group.cc#L102-L106
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/apis/python/src/tiledbsoma/soma_array.cc#L643
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/libtiledbsoma/src/soma/soma_group.cc#L233-L248
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/libtiledbsoma/src/soma/soma_array.cc#L1272-L1288
  • https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/apis/python/src/tiledbsoma/common.cc#L211-L225
  • Here the value type is supplied from the np.array at https://github.com/single-cell-data/TileDB-SOMA/blob/1.13.0/apis/python/src/tiledbsoma/_tdb_handles.py#L531-L536 and I was unable to find a dtype that did the right thing
  • Instead I have the mod on this PR, which says, string-valued metadata keys must use type TILEDB_STRING_UTF8
• R: At initial group-creation and array-creation times we have these:
  • https://github.com/single-cell-data/TileDB-SOMA/blob/ab0a5b59e3d54c03d27d60a6b3b049ebbf783b31/apis/r/R/SOMACollectionBase.R#L174-L179
  • https://github.com/single-cell-data/TileDB-SOMA/blob/ab0a5b59e3d54c03d27d60a6b3b049ebbf783b31/apis/r/R/SOMAArrayBase.R#L32-L40
  • https://github.com/single-cell-data/TileDB-SOMA/blob/ab0a5b59e3d54c03d27d60a6b3b049ebbf783b31/apis/r/R/TileDBGroup.R#L270-L293
  • https://github.com/single-cell-data/TileDB-SOMA/blob/ab0a5b59e3d54c03d27d60a6b3b049ebbf783b31/apis/r/R/TileDBArray.R#L105-L116
  • https://github.com/single-cell-data/TileDB-SOMA/blob/ab0a5b59e3d54c03d27d60a6b3b049ebbf783b31/apis/r/R/RcppExports.R#L73-L75
  • https://github.com/single-cell-data/TileDB-SOMA/blob/ab0a5b59e3d54c03d27d60a6b3b049ebbf783b31/apis/r/src/metadata.cpp#L164-L168
• R: subsequentpost-create metadata updates: same path

As a result:

• On initial object creation, string metadata values are correctly UTF-8 from Python or R
• Subsequent post-create metadata update, they were incorrectly non-UTF-8 from Python

Confounding circumstances:

• How these print from TileDB-SOMA-Py
• How these print from TileDB-SOMA-R
• How these print from TileDB-Py
• I found it easiest, as in the gist https://gist.github.com/johnkerl/a9eb64de62f881e80cd8e7ee54aa1c5c, to use TileDB-Py for readback:
  • Initial object-creation-time metadata reads back as "foo"
  • Post-create updated metadata reads back as b"foo" ...
  • ... until this PR

Changes:

Write post-create metadata updates from Python correctly using UTF-8 types.

Notes for Reviewer:

After this PR is merged I'll do cross-language tests in apis/system/tests to automate the kinds of things shown at gist https://gist.github.com/johnkerl/a9eb64de62f881e80cd8e7ee54aa1c5c

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.03%. Comparing base (ab0a5b5) to head (69c79d5). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2900 +/- ## ========================================== + Coverage 89.88% 90.03% +0.15% ========================================== Files 37 37 Lines 3925 3925 ========================================== + Hits 3528 3534 +6 + Misses 397 391 -6 ``` | [Flag](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2900/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | Coverage Δ | | |---|---|---| | [python](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2900/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | `90.03% <ø> (+0.15%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data#carryforward-flags-in-the-pull-request-comment) to find out more. | [Components](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2900/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | Coverage Δ | | |---|---|---| | [python_api](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2900/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | `90.03% <ø> (+0.15%)` | :arrow_up: | | [libtiledbsoma](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2900/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | `∅ <ø> (∅)` | |