fix(python): Address issue with read_database draining iter_batches early

[alexander-beedie]

Closes #15470 and closes #15469.

The generator was inadvertently being drained on the first call by a rogue "list" invocation - while it was correctly using fetchmany internally, it should only have been retrieving one batch per iteration, not retrieving all batches and then iterating (possibly something I was doing while debugging or refactoring that accidentally made it into a release 🤦).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.15%. Comparing base (31df06d) to head (f26c340).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15504      +/-   ##
==========================================
+ Coverage   81.14%   81.15%   +0.01%     
==========================================
  Files        1362     1362              
  Lines      174951   174951              
  Branches     2533     2533              
==========================================
+ Hits       141960   141987      +27     
+ Misses      32508    32482      -26     
+ Partials      483      482       -1     

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[stinodego]

Thanks for the fix!