feat(feature-activation): implement feature service

[glevco]

Depends on #623

This is an exact copy of #613, since it was merged in the incorrect order and reverted.

Acceptance Criteria

• Implement Block.get_feature_activation_bits() method and tests
• Implement FeatureService class and tests

[codecov]

Codecov Report

Merging #639 (7a84f43) into master (e80309e) will increase coverage by 0.04%.
The diff coverage is 97.75%.

❗ Current head 7a84f43 differs from pull request most recent head cf1a728. Consider uploading reports for the commit cf1a728 to get more accurate results

@@            Coverage Diff             @@
##           master     #639      +/-   ##
==========================================
+ Coverage   83.93%   83.97%   +0.04%     
==========================================
  Files         241      243       +2     
  Lines       20134    20223      +89     
  Branches     2742     2757      +15     
==========================================
+ Hits        16899    16982      +83     
- Misses       2638     2640       +2     
- Partials      597      601       +4     

Impacted Files	Coverage Δ
hathor/feature_activation/feature_service.py	97.26% <97.26%> (ø)
...or/feature_activation/model/feature_description.py	100.00% <100.00%> (ø)
hathor/transaction/block.py	91.19% <100.00%> (+0.48%)	⬆️

... and 5 files with indirect coverage changes