remove early stopping tracking from internal debugger

[awaelchli]

What does this PR do?

Follow up to #9188, #9326

Replaces the calls to the internal dev debugger in the early stopping callback. Tests are updated to cover what the "debugger" offered for tracking the calls inside the callback.
This is just one step towards removing the InternalDebugger completely in favor of proper unit testing.

Does your PR introduce any breaking changes? If yes, please list them.

No, the "InternalDebugger" is internal as the name suggests.

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Did you have fun?

I made sure I had fun coding 🙃

[codecov]

Codecov Report

Merging #9327 (b130961) into master (cf1a589) will decrease coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #9327   +/-   ##
======================================
- Coverage      92%     92%   -0%     
======================================
  Files         178     178           
  Lines       14858   14852    -6     
======================================
- Hits        13709   13703    -6     
  Misses       1149    1149           

[tchaton]

LGTM !