*: support electra in existing codebase; tests

[KaloyanTanev]

On first look it seems like a big PR, but it consists of 2 main things:

1. Adding electra version support to all switch cases throughout the codebase.
2. Adding tests for electra + improving the test coverage of already existing versions.

category: feature
ticket: none

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
12.6% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 96.96970% with 2 lines in your changes missing coverage. Please review.

Please upload report for BASE (electra@af7658f). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
app/eth2wrap/synthproposer.go	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             electra    #3487   +/-   ##
==========================================
  Coverage           ?   57.27%           
==========================================
  Files              ?      218           
  Lines              ?    33702           
  Branches           ?        0           
==========================================
  Hits               ?    19304           
  Misses             ?    12387           
  Partials           ?     2011           

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