InitialProtocolState refactor and epoch protocol sub-state rename

[jordanschalm]

This PR addresses the following item from #5666:

I find it super confusing / misleading that Snapshot.EpochProtocolState().Entry() is defined through the InitialProtocolState interface. The InitialProtocolState is very clear in its documentation that it (quote) "returns constant data for given epoch." Therefore, the only possible conclusion is also that Entry returns the DynamicProtocolState as specified initially by the Epoch Setup and Commit events. However, the implementations always return the DynamicProtocolState as of the specified block. (for further details and discussion, see #5650)

Suggestions: (discussion April 15th, Yurii, Jordan, Alex)

• merge InitialProtocolState interface into DynamicProtocolState EpochProtocolState
• whenever we are referring to Epoch-sub-state, we should explicitly refer to it using "Epoch..."

Changes

• Combines InitialProtocolState with DynamicProtocolState, renames combined type to EpochProtocolState
• Broadly speaking, renames types and variablesg which were previously referred to as "Protocol State", to "Epoch Protocol State"

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 71.15385% with 60 lines in your changes are missing coverage. Please review.

Project coverage is 55.79%. Comparing base (1ac121d) to head (3cc4dde).
Report is 19 commits behind head on master.

Files	Patch %	Lines
cmd/scaffold.go	0.00%	21 Missing ⚠️
utils/unittest/fixtures.go	0.00%	11 Missing ⚠️
model/flow/protocol_state.go	41.17%	10 Missing ⚠️
storage/badger/epoch_protocol_state.go	76.47%	8 Missing ⚠️
state/protocol/inmem/epoch_protocol_state.go	87.50%	2 Missing and 2 partials ⚠️
integration/testnet/container.go	0.00%	2 Missing ⚠️
state/protocol/badger/snapshot.go	87.50%	2 Missing ⚠️
state/protocol/protocol_state/epochs/factory.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5968      +/-   ##
==========================================
- Coverage   55.82%   55.79%   -0.04%     
==========================================
  Files        1129     1129              
  Lines       89260    89330      +70     
==========================================
+ Hits        49829    49840      +11     
- Misses      34677    34735      +58     
- Partials     4754     4755       +1     

Flag	Coverage Δ
unittests	55.79% <71.15%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[AlexHentschel]

Thank you. This refactoring removes a large amount of ambiguity in my opinion. Great work 👏 .

Unfortunately, there are some remaining areas, where we are actually referring to the epoch sub-state (of the overall protocol state) but Interface and method inputs still only talk about the "Protocol State". I think this is particularly dangerous in case of IDs because we have a the filed ProtocolStateID in the block Payload, which is identical naming to the epoch sub-state's ID for the storage layer and therefore very easily confused. I tried to add extensive comments in all places that I found. Though, if you could take a second look that I didn't miss anything that would be appreciated.

Not sure, but it might be best to first merge this PR and then follow up with a second one doing the renaming, because there are a lot of files changed already in this PR. If we do that in two PRs, I am happy to take a second pass. But I am also totally happy if you just do the renaming at the end of this PR before merging. It doesn't have to be perfect, as long as most places in the respective storage layer abstraction actually talk about the epoch sub-state, I think it is fine if we missed a few occurrences that still use "protocol state". It will be clear from context.

Happy to help with the renaming ... it might touch a lot of code to get it consistent.

[durkmurder]

Very nice PR, extremely solid refactoring which brings consistency in the code base. Well done!