Add SNOS RPC method duration metrics

[heemankv]

Summary

• add a dedicated pathfinder_snos_rpc_method_duration_seconds histogram for SNOS-facing RPC methods
• record only the low-cardinality method label for starknet_getStorageProof, starknet_getClass, and starknet_getClassHashAt
• update the existing Docker workflow so manual dispatch builds a Madara-style GHCR image for linux/amd64

Image

• Built successfully via GitHub Actions run: https://github.com/karnotxyz/pathfinder/actions/runs/28108834120
• Image: ghcr.io/karnotxyz/pathfinder:manual-58f395b
• Digest: sha256:7919a3d53714e43b7554b5ab03bb10ae67d8ca6a48bc2e299daa97bdfd6e5c59

Validation

• cargo check -p pathfinder-rpc

Notes

• The manual Docker path uses the Blacksmith 8-vCPU Ubuntu runner and explicitly builds linux/amd64, matching the effective architecture of Madara manual image builds.

[heemankv]

Closing this old-base PR to avoid deploying a Pathfinder v0.21-line image by mistake. The live-safe v0.22.3 Karnot branch PR is #12: #12