feat(metrics): switch to metrics-exporter-prometheus and histogram support in FFI

[AminR443]

This PR replaces the custom text recorder with metrics-exporter-prometheus::PrometheusRecorder, configures histograms and renders metrics via the Prometheus handle. It includes histogram timing metrics for propose/commit/batch operations alongside existing counters. Tested through the Go metrics test to expect the new histogram metrics.

Note: This drops unused chrono/metrics-util deps.

[github-actions]

Metrics Change Detection ⚠️

This PR contains changes related to metrics:

+            histogram!("firewood.ffi.commit_ms_bucket").record(commit_time.as_f64() * 1000.0);
-        counter!("firewood.ffi.batch_ms").increment(start_time.elapsed().as_millis());
+        counter!("firewood.ffi.batch_ms").increment(elapsed.as_millis());
+        histogram!("firewood.ffi.batch_ms_bucket").record(elapsed.as_f64() * 1000.0);
+            metrics::histogram!("firewood.ffi.commit_ms_bucket")
+        histogram!("firewood.ffi.propose_ms_bucket").record(propose_time.as_f64() * 1000.0);

However, the dashboard was not modified.

You may need to update benchmark/Grafana-dashboard.json accordingly.

---

This check is automated to help maintain the dashboard.

[rkuris]

Much simpler!