Mark evaluation epoch loops attributes as protected

[carmocca]

What does this PR do?

We forgot to mark these as protected. Follows the same pattern as in PredictionEpochLoop.

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

Users relying on these will fail. But these should have been protected from the start. This is okay as the loop refactor is unreleased.

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[codecov]

Codecov Report

Merging #8420 (8d30dc1) into master (74a09a2) will decrease coverage by 4%.
The diff coverage is 92%.

@@           Coverage Diff           @@
##           master   #8420    +/-   ##
=======================================
- Coverage      92%     88%    -4%     
=======================================
  Files         216     216            
  Lines       14112   14109     -3     
=======================================
- Hits        13017   12421   -596     
- Misses       1095    1688   +593     

[tchaton]

LGTM !