solana-rpc: first non-EVM chain in the RPC cluster (bench 075)

[Flotapponnier]

Summary

• Harness: Chain.Kind field selects the probe path. Solana rows use getSlot at processed commitment (rotating id, numeric slot parsing), slot-based staleness (300 slots ~ 2 min vs the cross-provider tip), archive-depth loop skipped (no keyless Solana equivalent, disclosed)
• Cohort: 5 keyless endpoints live-verified (Solana Labs official, PublicNode, Lava, LeoRPC FREE key disclosed, Solana Vibe Station); 10+ candidates excluded with verified refusals (dRPC paid-only, Ankr 403, OnFinality 429, Helius key-gated...)
• Spec: benchmarks/solana-rpc.yml (075), same shape as the per-chain EVM pages, rank matrix pinned to the keyless provider set so the keyed staging cohort (alchemy/chainstack/helius on chain=solana) never leaks in
• Gated in REMOVED_BENCH_SLUGS (staging pipeline); no cache key bump needed when adding a gated bench. /rpc hub auto-discovers the -rpc slug
• Recording rules are chain-agnostic, nothing to change VPS-side