Add test coverage to ensure that SQL tracker wrappers are applied only once to database cursors

[jayaddison]

This is an attempt to add test coverage for the behaviour discovered in #1239 and addressed in #1475.

The idea is to patch the state.Wrapper method that is called to add each wrapping layer, and count the number of calls for both chunked and non-chunked types of cursor (across all database provider implementations).

cc @saemideluxe

[tim-schilling]

Thanks for this @jayaddison. Did you happen to run these tests before 1475 was merged to verify that this would catch the duplicates?

[jayaddison]

@tim-schilling Although I only learned about the problem after a fix had been found (always nice to learn that a bug has already been solved), yep I did run this test coverage on a version of the code without the fix in place, to make sure that it failed before-the-fix and passes after-the-fix (albeit a small modification required, in honesty partly due to issues encountered with Python mock/patching.. see #1479).

[codecov]

Codecov Report

Merging #1478 (ca93f67) into main (77bbc8a) will increase coverage by 0.10%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1478      +/-   ##
==========================================
+ Coverage   86.27%   86.38%   +0.10%     
==========================================
  Files          35       35              
  Lines        1858     1858              
  Branches      261      261              
==========================================
+ Hits         1603     1605       +2     
+ Misses        182      181       -1     
+ Partials       73       72       -1     

Impacted Files	Coverage Δ
debug_toolbar/panels/profiling.py	88.39% <0.00%> (+1.78%)	⬆️

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