bench: add flashblock candidate execution bench gate (#564)

Author: julio4

crates/op-rbuilder/Cargo.toml

@@ -168,6 +168,8 @@ http-body-util.workspace = true
 [features]
 default = ["jemalloc"]
 
+bench-internals = []
+
 jemalloc = [
     "dep:tikv-jemallocator",
     "reth-cli-util/jemalloc",
@@ -193,6 +195,11 @@ loki = ["tracing-loki", "telemetry"]
 name = "bench_flashblocks_state_root"
 harness = false
 
+[[bench]]
+name = "bench_build_candidate"
+harness = false
+required-features = ["bench-internals"]
+
 [[bin]]
 name = "op-rbuilder"
 path = "src/bin/op-rbuilder/main.rs"