Replace Holesky with Hoodi across codebase

[doocho]

Summary

Update code, examples, and docs to use the Hoodi testnet instead of Holesky in preparation for Holesky’s sunset.

Changes

• README: replace Holesky guidance with Hoodi, update network list and checkpoint example.
• ethereum/config/checkpoints.rs: default checkpoint fallback networks now include Hoodi (replacing Holesky).
• ethereum/tests/checkpoints.rs: assertions and fetches updated to Hoodi.
• examples/checkpoints.rs: example updated to fetch Hoodi checkpoint.
• helios-ts/src/ethereum.rs (WASM): accepted networks now "mainnet" | "sepolia" | "hoodi"; uses networks::hoodi().
• helios-ts/lib.ts: network docs/types prefer "hoodi"; "holesky" marked as deprecated in comments.

Motivation & Context

Holesky testnet is being sunset. Hoodi testnet replaces it. This PR guides users to the new testnet and updates defaults to align with current network support.

Breaking Changes

• JS/WASM provider: passing "holesky" to the Ethereum client now errors; use "hoodi" instead.
• Checkpoint fallback defaults no longer query Holesky; they query Hoodi.

[doocho]

@ncitron