…idator (#591)

* feat: add benchmark workflow for rbuilder with base-reth-node validator

Adds a GitHub Actions workflow that benchmarks rbuilder as sequencer
with base-reth-node (built from this repo) as the validator node.

The workflow:
- Builds base-reth-node with maxperf profile
- Builds reth and rbuilder dependencies (with caching)
- Runs transfer throughput benchmark (10 blocks, 1B gas limit)
- Uploads benchmark output and HTML report as artifacts

* refactor: combine binary builds to share compiled dependencies

- Build base-reth-node and rbuilder in a single job to share common crates
- Remove reth build since it's not needed for this benchmark

* feat: cache binaries by commit SHA to avoid rebuilds

Skip expensive builds when the same commit SHA and rbuilder version
have already been built. All build steps are conditional on cache miss.

* perf: cache binaries by source hash instead of commit SHA

Use hash of Cargo.toml, Cargo.lock, crates/, and bin/ directories
instead of commit SHA. This allows iterating on the benchmark
workflow without triggering binary rebuilds.

* Update to base-builder and remove checkout step

* Debug log level

* Use test branch

* switch back

* Use base-builder naming instead of rbuilder