chore: add persist and RootStore metrics

[RodrigoVillar]

Why this should be merged

With the time-to-persist now decoupled from the time-to-commit, it would be great if we could capture data on how long it takes to persist + other similar processes.

How this works

• Adds timer to track how long it takes to persist
• Adds timer to track how long it takes to persisting root addresses to RootStore
• Adds counter to track how many times we block on commit

How this was tested

CI

[github-actions]

Metrics Change Detection ⚠️

This PR contains changes related to metrics:

+    describe_counter!(
+    describe_counter!(PERSIST_TOTAL, "Number of persist operations");
+    describe_counter!(PERSIST_TOTAL_MS, "Persist latency (ms)");
+    describe_counter!(PERSIST_ROOT_STORE, "Number of root store save operations");
+    describe_counter!(PERSIST_ROOT_STORE_MS, "Root store save latency (ms)");

However, the dashboard was not modified.

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

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This check is automated to help maintain the dashboard.

[RodrigoVillar]

Happy to add these metrics to our existing local dashboard if requested, but with @Elvis339 creating a new set of dashboards, it might make more sense to add these new metrics there rather than migrating.