feat: Signer signature count endpoint

[jbencin]

Description

Add RPC endpoint /v3/signer/{signer_pubkey}/{reward_cycle} that returns number of blocks signed by signer during given reward cycle

Applicable issues

• fixes #5106

Additional info (benefits, drawbacks, caveats)

Someone with more experience with chainstate DB and SQL in general please double-check the schema migration and queries

Progress

• [x] Add signer_stats table to chainstate DB
• [x] Update signer_stats database in append_block()
• [x] Add endpoint to query signer_stats table
• [x] Integration test

Checklist

• [x] Test coverage for new or modified code paths
• [x] Changelog is updated
• [x] Required documentation changes (e.g., docs/rpc/openapi.yaml and rpc-endpoints.md for v2 endpoints, event-dispatcher.md for new events)
• [x] New integration test(s) added to bitcoin-tests.yml

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
5 out of 6 committers have signed the CLA.

:white_check_mark: jbencin
:white_check_mark: kantai
:white_check_mark: jcnelson
:white_check_mark: saralab
:white_check_mark: obycode
:x: jferrant
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[jbencin]

but can you also add unit tests for the new handler. Each handler has a corresponding bundle of unit tests in stackslib/src/net/api/tests/

Sure, didn't know about these

[jferrant]

but can you also add unit tests for the new handler. Each handler has a corresponding bundle of unit tests in stackslib/src/net/api/tests/

Sure, didn't know about these

I added one @jbencin . Just relax and enjoy your time away! If @jcnelson needs further testing I can do :)