[c++] Use schema from tiledb::Array instead of ManagedQuery

[nguyenv]

Issue and/or context:

As part of work for #3053.

Changes:

This introduces a schema_ field to the SOMAArray, replacing any mq->schema() calls with schema_ directly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.78%. Comparing base (bf62847) to head (03befff).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3277      +/-   ##
==========================================
+ Coverage   83.67%   83.78%   +0.10%     
==========================================
  Files          51       51              
  Lines        5556     5556              
==========================================
+ Hits         4649     4655       +6     
+ Misses        907      901       -6     

Flag	Coverage Δ
python	83.78% <ø> (+0.10%)	⬆️

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Components	Coverage Δ
python_api	83.78% <ø> (+0.10%)	⬆️
libtiledbsoma	∅ <ø> (∅)

[johnkerl]

💫