tests(side-dag): implement missing side-dag related tests

[glevco]

Depends on #1069

Motivation

Implement missing tests for side-dag code.

Acceptance Criteria

• Change PoaBlockProducer so it does not require a HathorManager for initialization, and update builders accordingly. Add manager calculated property.
• Move PoA tests from test_block.py to test_poa.py.
• Implement new test_poa_block_producer.py and test_poa_simulation.py.
• Update test_verification.py.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[codecov]

Codecov Report

Attention: Patch coverage is 80.95238% with 8 lines in your changes missing coverage. Please review.

Project coverage is 85.04%. Comparing base (06a93b8) to head (59295e8).

Files	Patch %	Lines
hathor/builder/cli_builder.py	22.22%	5 Missing and 2 partials ⚠️
hathor/builder/builder.py	93.75%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1064      +/-   ##
==========================================
+ Coverage   84.60%   85.04%   +0.43%     
==========================================
  Files         309      309              
  Lines       23370    23396      +26     
  Branches     3523     3529       +6     
==========================================
+ Hits        19772    19896     +124     
+ Misses       2889     2799      -90     
+ Partials      709      701       -8     

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

The base branch was changed.