Bugfix/20002 superfluous query on head request in serializer

[xicond]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌
Fixed issues	#20055

[what-the-diff]

PR Summary

• Improved Data Serialization
  The method handling how data is serialized has been enhanced. Specifically, a property named 'totalCount' of the pagination information now reflects the full count of items from the data provider.

• Enhancements to Serializer Test
  Changes were executed in the Serializer's test suite for better functionality and comprehensive testing:

  • After the data provider is serialized, the test now confirms that the 'totalCount' appears in the response headers, ensuring that this information is correctly relayed.
  • A simulated version (mock object) of a data provider is created in testing, and this mocked version can reproduce expected outcomes when used.
  • The mocked data provider's pagination information can mirror the original data provider's, a feature exercised in the tests.
  • After the mock data provider is serialized, it's confirmed that the resulting response is empty (as expected).
  • An expectation has been added to ensure that certain method calls, particularly those involving data fetching, never happen within the mock data provider.
  • Contextual information such as posted form data or server data, used during the tests, is reset at the end of each test, maintaining test integrity.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (aa9adc8) 19.37% compared to head (9a2500d) 48.01%.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #20060       +/-   ##
===========================================
+ Coverage   19.37%   48.01%   +28.64%     
===========================================
  Files         445      445               
  Lines       43671    43897      +226     
===========================================
+ Hits         8461    21079    +12618     
+ Misses      35210    22818    -12392     

Files	Coverage Δ
framework/rest/Serializer.php	64.70% <100.00%> (+64.70%)	⬆️

... and 251 files with indirect coverage changes

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[samdark]

@xicond please add a line for CHANGELOG. Thanks.

[samdark]

Closed in favor of #20070