Add SNOS RPC method duration metrics

[heemankv]

Summary

• add a SNOS-specific RPC duration histogram for the three methods SNOS calls heavily
• record durations as seconds with only the method label to keep cardinality bounded
• add a manual GHCR image build path using Blacksmith and linux/amd64, matching the Madara-style manual build architecture

Metric

pathfinder_snos_rpc_method_duration_seconds{method}

Tracked methods:

• starknet_getStorageProof
• starknet_getClass
• starknet_getClassHashAt

Validation

• cargo check -p pathfinder-rpc

Image

Manual Docker workflow succeeded: https://github.com/karnotxyz/pathfinder/actions/runs/28110107948

Published image:

• ghcr.io/karnotxyz/pathfinder:manual-a9772c9
• digest: sha256:f7731714019b85e9379aef7e24af3e48d4216623e45c1bd1bb38e98d7693177a
• platform: linux/amd64