ignore --empty in unit test ref/source calls

[MichelleArk]

Resolves #10516

Problem

The unit test ref and source resolvers inherit from the base resolvers, meaning they were getting --empty limit filters applied when used with the --empty flag. This causes tests to fail / behave unpredictably since the mocked data is no longer used to configure the unit test!

Solution

overwrite resolve_limit in unit test ref/source resolvers directly to always return None (no limit filter applied), as they are never needed in the unit testing context.

Checklist

• I have read the contributing guide and understand what's expected of me.
• I have run this code in development, and it appears to resolve the stated issue.
• This PR includes tests, or tests are not required or relevant for this PR.
• This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• This PR includes type annotations for new and modified functions.

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.95%. Comparing base (db69473) to head (9f2316c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10764      +/-   ##
==========================================
- Coverage   88.97%   88.95%   -0.02%     
==========================================
  Files         181      181              
  Lines       22956    22983      +27     
==========================================
+ Hits        20424    20445      +21     
- Misses       2532     2538       +6     

Flag	Coverage Δ
integration	86.13% <83.33%> (-0.01%)	⬇️
unit	62.39% <66.66%> (-0.06%)	⬇️

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Components	Coverage Δ
Unit Tests	62.39% <66.66%> (-0.06%)	⬇️
Integration Tests	86.13% <83.33%> (-0.01%)	⬇️