feat(anvil): add debug_getRawHeader

[PelleKrab]

Superseded: Closed in favor of #67, which carries the debug APIs as verbatim upstream cherry-picks and keeps only the Beacon config spec endpoint fork-specific.

Motivation

Base proof witness construction needs the canonical RLP-encoded L1 block header selected by block ID.

Solution

Add geth-compatible debug_getRawHeader(BlockId) request handling and return the canonical RLP encoding of the selected header. Unknown blocks return null.

Stack

1. fix(deps): update ruint security advisory #63 — cargo-deny security prerequisite
2. feat(anvil): add debug_getRawHeader #61 — debug_getRawHeader ← this PR
3. feat(anvil): add debug_getRawReceipts #62 — debug_getRawReceipts
4. feat(anvil): add Beacon config spec endpoint #60 — Beacon /eth/v1/config/spec

Testing

• cargo test -p anvil --test it beacon_api::test_debug_get_raw_header -- --nocapture
• cargo fmt --all -- --check
• git diff --check

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[PelleKrab]

Superseded: debug_getRawHeader landed upstream in foundry-rs/foundry#15430 after our fork point, so #60 now carries it as a verbatim upstream cherry-pick instead of this hand-written implementation.