[Maikol]

Ports the EpochManager tests into horizon's Foundry suite, deploying the existing 0.7.6 EpochManager from the @graphprotocol/contracts build output, and deletes the TypeScript test it replaces. EpochManager moves into horizon later in this migration, so its tests land there first. Stacked on #1379.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.17%. Comparing base (38c8b81) to head (00c080e).
⚠️ Report is 3 commits behind head on chore/contracts-removal-phase-0.

Additional details and impacted files

@@                        Coverage Diff                        @@
##           chore/contracts-removal-phase-0    #1380    +/-   ##
=================================================================
  Coverage                            83.17%   83.17%            
=================================================================
  Files                                   81       81            
  Lines                                 5326     5326            
  Branches                              1132      973   -159     
=================================================================
  Hits                                  4430     4430            
  Misses                                 875      875            
  Partials                                21       21            

Flag	Coverage Δ
unittests	83.17% <ø> (ø)

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