[r] Push attrnames down to C++

[johnkerl]

#2406
#3058
[sc-55674]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.61%. Comparing base (0a9bf28) to head (7c70bbc).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3121      +/-   ##
==========================================
+ Coverage   86.56%   86.61%   +0.05%     
==========================================
  Files          47       47              
  Lines        4920     4924       +4     
==========================================
+ Hits         4259     4265       +6     
+ Misses        661      659       -2     

Flag	Coverage Δ
python	86.61% <ø> (+0.05%)	⬆️

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Components	Coverage Δ
python_api	86.61% <ø> (+0.05%)	⬆️
libtiledbsoma	∅ <ø> (∅)

[mojaveazure]

LGTM; please remember to bump the develop version, update the changelog, and 🚢

[johnkerl]

@mojaveazure my apologies -- I mixed up this PR and #3079 and did the DESCRIPITON / NEWS.md mods here:
https://github.com/single-cell-data/TileDB-SOMA/pull/3079/commits

[mojaveazure]

I'm not seeing an attrnames-pushdown in the changelog on 3079 https://github.com/single-cell-data/TileDB-SOMA/pull/3079/files#diff-e11a770652d5ae632a176b47454e64a9ab4168f1337594fa0022502100c0563e; can you add it as part of that PR so that we can have it in the changelog?

[johnkerl]

#3122