feat: add SNOS processing timing instrumentation

[heemankv]

Summary

• add a process-local RPC timing collector around retry-wrapped RPC calls
• log a SNOS timing summary with total elapsed, wall-clock RPC wait elapsed, local processing elapsed, RPC call count, and cumulative RPC call elapsed
• add extra proof-fetch/verification logs and tests for the timing collector

Testing

• cargo fmt --all
• cargo check -p rpc-client
• SNOS_RPC_URL=https://pathfinder-mainnet.d.karnot.xyz cargo test -p rpc-client

Notes

• cargo check -p generate-pie -p rpc-client is blocked in this local worktree because the Apollo build script requires cairo-compile on PATH; the existing sequencer_venv here does not provide cairo-compile.