Various improvements

[marcello33]

Description

In this PR, we implement some improvements to bor client:

1. improve the client for stable communication with heimdall via gRPC and better handle the errors/shutdown (# 12)
2. Fix checkpoint root computation (# 18)
3. Fix milestone whitelist concurrency bug (# 22)
4. Fix bor checkpoint merkle root reorg (# 23)

Changes

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Changes only for a subset of nodes

Checklist

• I have added at least 2 reviewer or the whole pos-v1 team
• I have added sufficient documentation in code
• I will be resolving comments - if any - by pushing each fix in a separate commit and linking the commit hash in the comment reply
• Created a task in Jira and informed the team for implementation in Erigon client (if applicable)
• Includes RPC methods changes, and the Notion documentation has been updated

Testing

• I have added unit tests
• I have added tests to CI
• I have tested this code manually on local environment
• I have tested this code manually on remote devnet using express-cli
• I have tested this code manually on amoy
• I have created new e2e tests into express-cli

[sonarqubecloud]

Quality Gate failed

Failed conditions
3.9% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 50.64103% with 77 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.38%. Comparing base (4c7bce2) to head (175c100).
⚠️ Report is 27 commits behind head on develop.

Files with missing lines	Patch %	Lines
consensus/bor/heimdallgrpc/client.go	0.00%	28 Missing ⚠️
consensus/bor/api.go	71.69%	11 Missing and 4 partials ⚠️
eth/ethconfig/config.go	0.00%	15 Missing ⚠️
eth/downloader/whitelist/milestone.go	62.85%	10 Missing and 3 partials ⚠️
eth/bor_checkpoint_verifier.go	76.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1950      +/-   ##
===========================================
+ Coverage    47.93%   48.38%   +0.45%     
===========================================
  Files          844      844              
  Lines       144067   144225     +158     
===========================================
+ Hits         69062    69788     +726     
+ Misses       70479    69804     -675     
- Partials      4526     4633     +107     

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