feat(serialization): add Exponential-Continuation Varint implementation

[jansegre]

Motivation

We've previously discussed about using an encoding that takes less bits for larger numbers. This PR introduces such encoding, that is based on LEB128 but uses a continuation bit every time the size doubles, not every time it increases by one byte, so it was named Exponential Continuation Varint (ECV) for the lack of a better name.

This PR purely introduces the new encoding and does not use it anywhere, so it is not a breaking change.

Acceptance Criteria

• Add ECV serialization encoder/decoder
• Add tests for both LEB128 and ECV

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	feat/ecv-serialization
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	1.95 m (+14.50%) Baseline: 1.70 m	1.53 m (78.60%)	2.04 m (95.42%)

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[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.80%. Comparing base (a9a0fb7) to head (c6eddd3).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
hathor/serialization/encoding/ecv.py	94.87%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1405      +/-   ##
==========================================
+ Coverage   85.76%   85.80%   +0.03%     
==========================================
  Files         430      431       +1     
  Lines       33054    33093      +39     
  Branches     5172     5179       +7     
==========================================
+ Hits        28349    28394      +45     
+ Misses       3667     3663       -4     
+ Partials     1038     1036       -2     

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