refactor(daa): externalize block dependencies

[glevco]

Depends on #909

Motivation

Change the DAA so it does not access the storage directly. Instead, block verification can pass pre-fetched dependencies through a new SimpleMemoryStorage. This will be useful for Multiprocess Verification.

Acceptance Criteria

• Create new SimpleMemoryStorage class that will be used for storing pre-fetched verification dependencies in memory.
• Change DAA methods calculate_block_difficulty and calculate_next_weight to accept a SimpleMemoryStorage, which is used to retrieve pre-fetched parent blocks.
• Update block's verify_weight to pre-fetch DAA dependencies.

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 84.05797% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 85.16%. Comparing base (443604f) to head (ae05d01).

Files	Patch %	Lines
...athor/transaction/storage/simple_memory_storage.py	75.55%	8 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #895      +/-   ##
==========================================
+ Coverage   85.02%   85.16%   +0.14%     
==========================================
  Files         294      295       +1     
  Lines       22801    22864      +63     
  Branches     3435     3443       +8     
==========================================
+ Hits        19386    19472      +86     
+ Misses       2726     2710      -16     
+ Partials      689      682       -7     

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