chore: migrate conformance test runner to tokio

Switch from async-std to tokio runtime and maintain rough test execution time
while simplifying the async implementation.

Ref: #2173

Author: rvagg

Cargo.lock

@@ -43,7 +43,8 @@ m2-native = []
 [dev-dependencies]
 env_logger = "0.11.8"
 criterion = { version = "0.5" }
-rayon = "1.10.0"
+tokio = { version = "1.45", features = ["rt-multi-thread", "macros", "sync"] }
+futures = "0.3.31"
 
 [[bin]]
 name = "perf-conformance"