core/consensus: refactor duration metric

[corverroos]

Refactors the consensus duration metric to duration=consensus_decided_at-consensus_proposed_at so that eager timer durations are reflected correctly since they start much earlier than normal timing strategies.

category: refactor
ticket: #2337

[codecov]

Codecov Report

Patch coverage: 86.95% and project coverage change: +0.02 🎉

Comparison is base (f6e7c24) 53.71% compared to head (03e27cf) 53.73%.

❗ Current head 03e27cf differs from pull request most recent head b820c4d. Consider uploading reports for the commit b820c4d to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2425      +/-   ##
==========================================
+ Coverage   53.71%   53.73%   +0.02%     
==========================================
  Files         199      198       -1     
  Lines       26467    26462       -5     
==========================================
+ Hits        14216    14220       +4     
+ Misses      10483    10479       -4     
+ Partials     1768     1763       -5     

Impacted Files	Coverage Δ
core/consensus/component.go	66.82% <86.95%> (+1.00%)	⬆️

... and 7 files with indirect coverage changes

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