refactor(sync-v2): Refactor sync_v2 agent to hold (block_height, block_id) information in an internal namedtuple

[msbrogli]

Motivation

Sync-v2 agent code uses the pair (block_height, block_hash) multiple times. So this PR refactors it to use a namedtuple BlockInfo (instead of handling with both information separately).

Acceptance Criteria

1. Add hathor.p2p.sync_v2.agent.BlockInfo.
2. Add hathor.p2p.sync_v2.agent.NodeBlockSync.get_my_best_block() method.
3. Refactor find_best_common_block() and run_sync_blocks() methds to use BlockInfo.
4. Rename variables (synced, not_synced) to (lo, hi) in the n-ary search.
5. There are two behavior changes in this PR: (i) change of keys in the get_status(), and (ii) using lo=0 instead of lo=self.synced_block.height.

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

All modified and coverable lines are covered by tests ✅

Comparison is base (20474fd) 84.56% compared to head (59d5104) 84.63%.

❗ Current head 59d5104 differs from pull request most recent head 89d347e. Consider uploading reports for the commit 89d347e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #829      +/-   ##
==========================================
+ Coverage   84.56%   84.63%   +0.07%     
==========================================
  Files         270      270              
  Lines       22291    22290       -1     
  Branches     3406     3404       -2     
==========================================
+ Hits        18850    18865      +15     
+ Misses       2769     2757      -12     
+ Partials      672      668       -4     

Files	Coverage Δ
hathor/p2p/sync_v2/agent.py	75.00% <100.00%> (+0.83%)	⬆️

... and 5 files with indirect coverage changes

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