docs(world-chain): add third-party benchmarks section

[Flotapponnier]

Adds a short "Third-Party Benchmarks" section to world-chain/resources.mdx, between the existing "Status Links" and "Documentation" sections.

Why this fits:

• The Resources page already lists external status monitoring (Alchemy status pages)
• OpenChainBench provides independent public RPC latency measurements for World Chain
• Developers evaluating World Chain endpoints benefit from a neutral third-party performance reference

What's added:

• One new H2 section with a single bullet
• Link to https://openchainbench.com/benchmarks/world-chain-rpc

About OpenChainBench: independent open-source project measuring public RPC endpoint latency across 22+ chains every minute from three regions (US East, EU West, Singapore). Data published under CC BY 4.0, Go harness open sourced on GitHub, no affiliation with any RPC provider.

Disclosure: I contribute to OpenChainBench. Happy to reword or drop entirely if this doesn't fit editorial guidelines.

[Flotapponnier]

Just bumping this in case it got buried under other PRs. Happy to adjust the wording or placement if that would help!