feat(sync, store)!: Remove adjacency requirement from Store.Append

[cristaloleg]

Overview

Things that gonna change after we drop adjacency requirement from Store.Append:

• Obviously dropping ErrNonAdjacent (breaking change).
• Store.Append comment is already outdated (looks like there were 2 return params)
• store.Store.Append will not verify for adjacency (obviously)
• Syncer.setSubjectiveHead will not verify for ErrNonAdjacent
• adjacency check is happening in sync instead of store.

Fixes #32

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 62.75%. Comparing base (88c5b8c) to head (5a10a68).
Report is 11 commits behind head on main.

❗ Current head 5a10a68 differs from pull request most recent head f10cce8

Please upload reports for the commit f10cce8 to get more accurate results.

Files	Patch %	Lines
sync/sync_store.go	56.25%	5 Missing and 2 partials ⚠️
store/heightsub.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #186      +/-   ##
==========================================
- Coverage   62.80%   62.75%   -0.05%     
==========================================
  Files          39       38       -1     
  Lines        3589     3587       -2     
==========================================
- Hits         2254     2251       -3     
- Misses       1160     1163       +3     
+ Partials      175      173       -2     

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[Wondertan]

Ok, so nothing really changes with this PR yet. We need to discuss what are there next changes in the Syncer