feat(core): Enable metrics for core package

[renaynay]

While we do plan to remove the bridge node type eventually, it's useful to have some visibility into the core package in the short term.

[codecov-commenter]

Codecov Report

Attention: 86 lines in your changes are missing coverage. Please review.

Comparison is base (3fde8c9) 51.67% compared to head (2737752) 51.38%.

Files	Patch %	Lines
core/listener_metrics.go	8.51%	43 Missing ⚠️
core/exchange_metrics.go	18.51%	21 Missing and 1 partial ⚠️
core/listener.go	52.63%	7 Missing and 2 partials ⚠️
core/exchange.go	60.00%	6 Missing and 2 partials ⚠️
core/option.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2863      +/-   ##
==========================================
- Coverage   51.67%   51.38%   -0.29%     
==========================================
  Files         167      170       +3     
  Lines       10812    10925     +113     
==========================================
+ Hits         5587     5614      +27     
- Misses       4729     4810      +81     
- Partials      496      501       +5     

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[Wondertan]

I realized that we don't need blockTime metric. The bridge node publishes headers through Subscriber, which goes through that validator, and time is tracked there on subscriber metrics. So effectively we will get the same time twice

[renaynay]

@Wondertan the reason i wanted to capture block time here is that it's the only way to know on the DA-side what the approximate block time is so that we can see if there's a difference between core network block time and DA header propagation time.

I removed it in this commit 403bc9a

[Wondertan]

I understand and it turns out we designed things in a way that we don't need to duplicate anything 😺

[Wondertan]

We should aim to include fetcher metrics here as well

[Wondertan]

Linter btw

[Wondertan]

LGTM