Consolidate locking mechanisms with stdlib Mutex
We're using three different locking mechanisms at the moment, ActorIsolated, LockIsolated, and QueueIsolated. We should use the new standard library Mutex instead.
Have to be aware of some pitfalls here, Mutex can apparently crash the compiler on Linux.
https://github.com/swift-server/swift-aws-lambda-runtime/blob/eb634fa9abcd178f9f86852ea0839109bd949a97/Sources/AWSLambdaRuntime/LambdaRuntime.swift#L30
See https://github.com/swiftlang/swift/issues/80036 and https://github.com/swiftlang/swift/issues/80020
Looks like the compiler crash happens on Mutex with generic types only https://github.com/swiftlang/swift/issues/78048
I also think https://github.com/swiftlang/swift/issues/80020 is not related to Mutex