More EpochResultStore refactors! 🎉

[carmocca]

What does this PR do?

Refactoring done while debugging #5521

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[codecov]

Codecov Report

Merging #5522 (e59c0c3) into release/1.2-dev (774e9bd) will increase coverage by 5%.
The diff coverage is 97%.

@@               Coverage Diff                @@
##           release/1.2-dev   #5522    +/-   ##
================================================
+ Coverage               83%     88%    +5%     
================================================
  Files                  181     181            
  Lines                12929   12742   -187     
================================================
+ Hits                 10771   11236   +465     
+ Misses                2158    1506   -652     

[tchaton]

Great refactor ! Let refactor info a proper structure as recommended by @ananthsub.

[Borda]

@carmocca mind check the conflicts so we can start review :]

[tchaton]

LGTM !