B16: Validate block lookup identities

[KillariDev]

Summary

• reject explicit block lookups when the RPC response identifies a different height
• apply the same invariant to replacement-transaction scans
• add focused direct-lookup and replacement-scan regression coverage

Why

An RPC endpoint could return a structurally valid block for the wrong height. The client previously accepted it, so callers could act on unrelated block data and replacement detection could report a transaction from a height it never requested.

Validation

• failing-first: bun test shared/ts/ethereum.test.ts --timeout=600000 (2 expected failures)
• bun test shared/ts/ethereum.test.ts --timeout=600000 (33 pass)
• bun run tsc
• bun run ensure-contract-artifacts && bun run check:shared-dependencies && bun run test:run -- --bail=1 --timeout=600000 (3252 pass, 16 skip)
• bun run format:check
• bun run check:changed
• bun run knip
• git diff --check

Final review: 100/100, no findings. Branch was current with origin/main at publication.