feat(proxyd): add flashblocks-aware routing

[paranoiacblack]

Description

• Adds flashblocks-aware routing. When eth_getBlockByNumber, eth_getTransactionCount, eth_getTransactionReceipt and eth_getBalance are called with "pending" block numbers on chains producing Flashblocks, the request will be answered by a flashblocks-aware backend.
• Adds configuration that enables flashblocks-aware routing.
• Adds configuration that allows specifying exactly one flashblocks-aware backend group.
• Adds logic to parse JSON-RPC request's method and parameters to determine if it should be sent to the flashblocks-aware backend group or to normally configured backend group for the rpc method mapping.

Tests

• Added tests for checking for pending JSON-RPC requests.
• Added integration tests for every request + param combination that can ask for information about the latest flashblock.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.17544% with 17 lines in your changes missing coverage. Please review.

Project coverage is 61.27%. Comparing base (7d490c1) to head (c331ee2).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
proxyd/rpc.go	63.33%	6 Missing and 5 partials ⚠️
proxyd/proxyd.go	45.45%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
- Coverage   61.32%   61.27%   -0.05%     
==========================================
  Files          80       80              
  Lines       10855    10901      +46     
==========================================
+ Hits         6657     6680      +23     
- Misses       3780     3795      +15     
- Partials      418      426       +8     

Flag	Coverage Δ
proxyd	71.46% <70.17%> (-0.23%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
proxyd/config.go	54.76% <ø> (ø)
proxyd/server.go	78.63% <100.00%> (+0.15%)	⬆️
proxyd/proxyd.go	55.91% <45.45%> (-0.25%)	⬇️
proxyd/rpc.go	83.47% <63.33%> (-6.64%)	⬇️

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.