[WIP] Improve sequencer metrics for block building duration

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Metrics] Improve sequencer metrics</issue_title>
<issue_description>Yes the idea was only to record the actual block building duration for blocks that get added to the chain. I think we could however also have a metric for block building regardless of whether they get added to the chain, and also for the duration between 2 consecutive block added to the chain.

Originally posted by @greged93 in #367 (comment)
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Comments on the Issue (you are @copilot in this section)

• Fixes [Metrics] Improve sequencer metrics #373

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