network: stateful vote compression

[cce]

Summary

This adds to #6276 a StatefulEncoder and StatefulDecoder, that compress votes using HPACK-style references to values from previous votes. It provides better than 50% compression given different table sizes.

Notes on memory vs bandwidth tradeoff and effectiveness of stateful vote compression are here: #6467

Test Plan

• Unit tests in vpack package
• Ensure full test coverage in vpack package

[codecov]

Codecov Report

Attention: Patch coverage is 98.43444% with 8 lines in your changes missing coverage. Please review.

Project coverage is 50.65%. Comparing base (18990e0) to head (571d707).
Report is 61 commits behind head on master.

Files with missing lines	Patch %	Lines
network/vpack/dynamic_vpack.go	97.97%	6 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6351      +/-   ##
==========================================
- Coverage   51.82%   50.65%   -1.17%     
==========================================
  Files         652      656       +4     
  Lines       87425   110899   +23474     
==========================================
+ Hits        45307    56177   +10870     
- Misses      39249    51858   +12609     
+ Partials     2869     2864       -5     

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

[Copilot]

Pull Request Overview

This pull request introduces dynamic vote compression functionality using StatefulEncoder and StatefulDecoder components that implement HPACK-style references to values from previous votes, providing over 50% compression efficiency with different table sizes.

• Adds StatefulEncoder/StatefulDecoder with LRU tables for caching commonly used values (addresses, public key/signature pairs)
• Implements a proposal window using HPACK-style indexing for proposal bundle compression
• Introduces delta encoding for round numbers and reference-based compression for repeated values

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
network/vpack/vpack.go	Updates header comment and refactors varuint parsing logic into a shared helper function
network/vpack/msgp.go	Adds msgpVaruintRemaining helper function and refactors readUintBytes to use it
network/vpack/dynamic_vpack.go	Core implementation of StatefulEncoder/StatefulDecoder with compression logic
network/vpack/lru_table.go	Implements 2-way set-associative LRU hash table for value caching
network/vpack/proposal_window.go	Implements HPACK-style sliding window for proposal bundle references
network/vpack/dynamic_vpack_test.go	Comprehensive tests for stateful encoding/decoding functionality
network/vpack/lru_table_test.go	Tests for LRU table operations including eviction and consistency
network/vpack/proposal_window_test.go	Tests for proposal window HPACK-style behavior