fix(metrics): pass metrics to mempool init

[artemijspavlovs]

PR Standards

Opening a pull request should be able to meet the following requirements

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this change passes the received metrics provider from function arguments down to dymint mempool creation. after enabling this, mempool size metric is available on the /metrics endpoint. Other metrics will come in a separate PR.

❯ curl localhost:2112/metrics | grep dymint
# TYPE dymint_mempool_size gauge
dymint_mempool_size 0

For Author:

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• Linked to Github issue with discussion and accepted design
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• Wrote unit and integration tests
• All CI checks have passed
• Added relevant godoc comments

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For Reviewer:

• confirmed the correct type prefix in the PR title
• Reviewers assigned
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After reviewer approval:

• In case targets main branch, PR should be squashed and merged.
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