fix(ws): Slow empty address verification on address subscription

[msbrogli]

Motivation

The current implementation of empty addresses was too slow. It was running in O(n) where n is the number of subscribed addresses. So, the time complexity to load a wallet was O(n^2) because the check was executed for each address.

This PR reduces the time complexity to O(m) where m is the number of empty addresses. So, the load time is reduced to O(nm). Notice that m < n / gap_limit.

Acceptance Criteria

1. Add a separate list of empty addresses.
2. On address subscription, add empty addresses to the empty address set.
3. Only validate the list of empty addresses if the empty address set is greater than the limit.

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

[github-actions]

Bencher Report

Branch	fix/ws-slow-empty-addr-verification
Testbed	ubuntu-22.04

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Benchmark	Latency	Benchmark Result minutes (m) (Result Δ%)	Lower Boundary minutes (m) (Limit %)	Upper Boundary minutes (m) (Limit %)
sync-v2 (up to 20000 blocks)	📈 view plot 🚷 view threshold	1.50 (-9.11%)	1.49 (99.02%)	1.82 (82.63%)

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[codecov]

Codecov Report

Attention: Patch coverage is 21.42857% with 11 lines in your changes missing coverage. Please review.

Project coverage is 83.58%. Comparing base (aede16a) to head (a3bf50c).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
hathor/websocket/factory.py	15.38%	9 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1203      +/-   ##
==========================================
- Coverage   83.63%   83.58%   -0.06%     
==========================================
  Files         320      320              
  Lines       24540    24551      +11     
  Branches     3762     3764       +2     
==========================================
- Hits        20524    20520       -4     
- Misses       3255     3267      +12     
- Partials      761      764       +3     

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