tools: add OpenChainBench to on-chain analytics

[Flotapponnier]

Adds OpenChainBench to the Analytics > On-chain analytics section, alongside ETH Gas.watch.

OpenChainBench is the missing infrastructure layer in this list: while Dune, Glassnode and Nansen cover token/protocol-level data, nobody listed here answers the lower-level questions that matter for trading infrastructure — which RPC is fastest, which gas oracle is accurate, how long does finality actually take on each chain.

Concretely:

• RPC latency benchmarks (p50/p90/p99) across 15+ providers per chain, probed every minute from US East, EU West and Singapore
• Gas oracle accuracy vs actual next-block inclusion
• L1/L2 finality wall-clock times (not whitepaper claims)
• 76 benchmarks across 22+ chains (Ethereum, Solana, Arbitrum, Base, Optimism, BNB, Avalanche and more)
• Open-source Prometheus harnesses, data published under CC BY 4.0

I maintain OpenChainBench. Happy to adjust wording or placement.

[Flotapponnier]

Friendly bump. Happy to adjust the wording, section, or the linked page if that helps this land. Thanks for your work on this project!