feat(feature-activation): bit count optimization

[glevco]

Implements the suggestion in #613 (comment)

Acceptance Criteria

• Implement new get_bit_list() utils function
• Create new TransactionMetadata.feature_activation_bit_counts attribute
• Implement new BaseTransaction.calculate_feature_activation_bit_counts() abstract method and concrete implementations on Block and Transaction
• Add feature_activation_bit_counts to BaseTransaction.get_metadata() and BaseTransaction.update_initial_metadata()
• Update FeatureService to use the feature_activation_bit_counts metadata attribute instead of calculating the bit count itself

[codecov]

Codecov Report

Merging #633 (0bc0df8) into master (f8796eb) will decrease coverage by 0.35%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #633      +/-   ##
==========================================
- Coverage   83.97%   83.63%   -0.35%     
==========================================
  Files         245      246       +1     
  Lines       20299    20339      +40     
  Branches     2763     2767       +4     
==========================================
- Hits        17047    17011      -36     
- Misses       2657     2742      +85     
+ Partials      595      586       -9     

Impacted Files	Coverage Δ
hathor/conf/unittests.py	100.00% <100.00%> (ø)
hathor/feature_activation/feature_service.py	96.82% <100.00%> (-0.44%)	⬇️
hathor/transaction/base_transaction.py	91.45% <100.00%> (+0.01%)	⬆️
hathor/transaction/block.py	92.05% <100.00%> (+0.86%)	⬆️
hathor/transaction/transaction_metadata.py	90.68% <100.00%> (+0.23%)	⬆️
hathor/utils/int.py	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes