Add prometheus

[Brindrajsinh-Chauhan]

This PR adds Prometheus metrics to the remote signer to have monitoring of this components

Metrics include

• Process metrics
• Golang metrics
• And some custom metrics like

# HELP arc_remote_signer_request_total Total number of signing requests
# TYPE arc_remote_signer_request_total counter
arc_remote_signer_request_total{type="publickey"} 1
# HELP arc_remote_signer_request_total_success Total number of successful signing requests
# TYPE arc_remote_signer_request_total_success counter
arc_remote_signer_request_total_success{type="publickey"} 1

[Cassxbt]

Normal shutdown can terminate the process here.

I reproduced this against f19a29a with a focused package test: Run() starts Serve() in a goroutine, then Shutdown() manually closes s.listener before calling s.server.Shutdown(...). That makes Serve() return:

accept tcp 127.0.0.1:...: use of closed network connection

That error is not http.ErrServerClosed, so the goroutine reaches log.Fatalf("failed to serve: %v", err) and exits the process during a normal lifecycle shutdown.

The same path also ignores the caller-provided shutdown context by calling s.server.Shutdown(context.Background()).

Minimal fix is to let http.Server.Shutdown(ctx) close the listener and honor the provided context:

func (s *RunnableImpl) Shutdown(ctx context.Context) error {
	for _, fn := range s.beforeShutdownFns {
		fn()
	}

	log.Printf("initiating graceful shutdown of http server at %s", s.listener.Addr().String())
	if err := s.server.Shutdown(ctx); err != nil {
		return err
	}
	log.Printf("http server gracefully stopped")
	return nil
}

Focused verification:

• current PR code fails with failed to serve: accept tcp ...: use of closed network connection
• the change above passes go test ./internal/common/http/server

go test ./... is currently blocked by missing generated proto/pb, so I scoped verification to the affected HTTP package.

[Brindrajsinh-Chauhan]

Thank you for the feedback. I have pushed another commit to address the comment. Would be grateful if you could review it again.

Thanks again