Fix high cardinality metrics by removing unbounded labels

[fridrik01]

This PR addresses a metrics issue by removing unbounded labels from Prometheus metrics that can cause cardinality explosion and degrade system performance in our monitoring systems.

I believe it should be fine to remove these labels as we should have information about them in our logs/loki.

Note: if any Grafana dashboards relied on these labels, they may need to be updated to reflect the new metric structure.

[codecov]

Codecov Report

❌ Patch coverage is 70.83333% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.11%. Comparing base (5fe4aab) to head (a459d97).

Files with missing lines	Patch %	Lines
execution/engine/metrics.go	60.00%	8 Missing ⚠️
beacon/blockchain/deposit.go	0.00%	2 Missing ⚠️
beacon/blockchain/metrics.go	85.71%	2 Missing ⚠️
beacon/blockchain/payload.go	75.00%	1 Missing ⚠️
execution/engine/engine.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@                     Coverage Diff                     @@
##           blobreactor-prometheus2    #2967      +/-   ##
===========================================================
- Coverage                    64.15%   64.11%   -0.05%     
===========================================================
  Files                          371      371              
  Lines                        18597    18591       -6     
===========================================================
- Hits                         11931    11919      -12     
- Misses                        5759     5764       +5     
- Partials                       907      908       +1     

Files with missing lines	Coverage Δ
state-transition/core/metrics.go	94.80% <100.00%> (-0.07%)	⬇️
state-transition/core/state_processor_payload.go	63.86% <100.00%> (ø)
beacon/blockchain/payload.go	52.86% <75.00%> (-0.30%)	⬇️
execution/engine/engine.go	59.06% <50.00%> (ø)
beacon/blockchain/deposit.go	45.16% <0.00%> (-0.88%)	⬇️
beacon/blockchain/metrics.go	97.26% <85.71%> (ø)
execution/engine/metrics.go	67.85% <60.00%> (-0.43%)	⬇️

... and 2 files with indirect coverage changes

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