[metrics] metrics + metrics-exporter-prometheus not declared in workspace.dependencies

[obchain]

Refs #50

File: Cargo.toml (root)

Problem

charon-metrics declares dependencies on metrics + metrics-exporter-prometheus (or whichever crate is used) directly with version strings instead of via [workspace.dependencies]. Project convention is workspace-wide deps with single version source.

Fix

Add to root Cargo.toml [workspace.dependencies]:

metrics = "0.23"
metrics-exporter-prometheus = "0.15"

Reference in charon-metrics/Cargo.toml as { workspace = true }.

[obchain]

Fixed on feature branch; see feat/22-prometheus-metrics / feat/26-grafana-dashboard commits.