feat(bench): add replay-reorg command for benchmarking reorgs

[decofe]

Adds a new reth-bench replay-reorg subcommand that replays a reorg between two existing block hashes.

How it works

Given two competing chain tips (--tip-a and --tip-b), the command:

1. Walks both tips back to find their common ancestor (number-aligned for efficiency)
2. Builds fork A as canonical by sending newPayload + forkchoiceUpdated
3. Imports fork B blocks as side-chain (newPayload only)
4. Triggers the reorg via a single forkchoiceUpdated switching head to fork B

Reports per-phase and per-call latency, with the reorg FCU latency called out separately.

Flags

• --tip-a / --tip-b: the two competing chain tip hashes
• --order a-then-b|b-then-a: which fork to build canonical first (default: a-then-b)
• --fcu-mode tip-only|per-block: FCU after every block vs only at the tip during canonical build (default: tip-only)
• --max-depth: cap on ancestor search depth (default: 4096)
• --reth-new-payload: use reth_newPayload endpoint for server-side timing

Example

reth-bench replay-reorg \\
  --rpc-url http://localhost:8545 \\
  --engine-rpc-url http://localhost:8551 \\
  --jwt-secret ~/.local/share/reth/mainnet/jwt.hex \\
  --tip-a 0xaaa... --tip-b 0xbbb...

Co-Authored-By: Dan Cline 6798349+Rjected@users.noreply.github.com

Prompted by: Dan

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reth-bench: minor
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Added `replay-reorg` subcommand to `reth-bench` for benchmarking chain reorgs. The command discovers the common ancestor of two competing chain tips, builds one fork as canonical via the Engine API, imports the competing fork, then triggers a reorg via `forkchoiceUpdated`. Supports fetching blocks from EL RPC, pre-downloaded JSON files, or a Dora beacon explorer.

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