chore: avoid using RocksDB keys estimation

[luislhl]

This was created from the discussion #490 (comment)

Acceptance Criteria

We should prefer to use the InfoIndex when possible to get a count of the number of vertices, instead of relying on specific logic for each kind of storage to count the number of vertices.

Specifically, we notices that the specific logic we had to count the number of vertices in RocksDB was not accurate. See the link above for more info.

This change highlighted a bug we had in the InfoIndex count of txs/blocks when a split-brain happens. It was counting the txs/blocks of the winner chain twice when the nodes connected again and the winner was chosen. We had to fix this bug in this PR as well.

[codecov]

Codecov Report

Merging #496 (dd3826e) into dev (6bfc2f9) will decrease coverage by 0.12%.
The diff coverage is 81.33%.

@@            Coverage Diff             @@
##              dev     #496      +/-   ##
==========================================
- Coverage   83.69%   83.57%   -0.13%     
==========================================
  Files         184      187       +3     
  Lines       16452    16829     +377     
  Branches     2520     2590      +70     
==========================================
+ Hits        13770    14065     +295     
- Misses       2230     2300      +70     
- Partials      452      464      +12     

Impacted Files	Coverage Δ
hathor/transaction/storage/binary_storage.py	90.25% <43.75%> (-7.59%)	⬇️
hathor/transaction/storage/compact_storage.py	89.93% <43.75%> (-6.60%)	⬇️
hathor/transaction/storage/cache_storage.py	91.97% <57.14%> (-2.73%)	⬇️
hathor/transaction/storage/transaction_storage.py	89.79% <63.00%> (-5.33%)	⬇️
hathor/transaction/storage/rocksdb_storage.py	94.73% <68.18%> (-5.27%)	⬇️
hathor/event/storage/rocksdb_storage.py	83.63% <74.28%> (-16.37%)	⬇️
...tion/storage/migrations/add_min_height_metadata.py	80.00% <80.00%> (ø)
hathor/transaction/storage/migrations/__init__.py	82.14% <82.14%> (ø)
hathor/indexes/mempool_tips_index.py	93.57% <88.46%> (-2.17%)	⬇️
hathor/event/storage/memory_storage.py	93.10% <90.00%> (-6.90%)	⬇️
... and 26 more

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