Apply limit to IQueryable in FirstOrDefault/SingleOrDefaultMiddleware

[glen-84]

Summary of the changes (Less than 80 chars)

• Applied limit to IQueryables in FirstOrDefaultMiddleware and SingleOrDefaultMiddleware.
  • Take(1) for FirstOrDefault.
  • Take(2) for SingleOrDefault.

Closes #5566

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Notes:

• I'm not sure why the tests use AsExecutable, since it's more common to return an IQueryable.
  • I've removed this so that the IAsyncEnumerable path is followed, but let me know if it should be restored for some reason.
• The application of the limit is slightly awkward – I'm assuming that non-IQueryable IAsyncEnumerables still need to be handled, otherwise the switch/case could be simplified.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 76.42%. Comparing base (ad98734) to head (0feca76).

Files	Patch %	Lines
...src/Data/Projections/FirstOrDefaultMiddleware~1.cs	0.00%	6 Missing ⚠️
...rc/Data/Projections/SingleOrDefaultMiddleware~1.cs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6833      +/-   ##
==========================================
- Coverage   78.91%   76.42%   -2.49%     
==========================================
  Files        2605     2622      +17     
  Lines      130418   130981     +563     
==========================================
- Hits       102915   100108    -2807     
- Misses      27503    30873    +3370     

Flag	Coverage Δ
unittests	76.42% <0.00%> (-2.49%)	⬇️

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