Possible ways to optimize HashMap<MessageId, Message>

[rukai]

HashMap<MessageId, Message> is now a common idiom in transforms for keeping track of a generated response that needs to replace the response to a certain request.
In order to optimize this I have a few ideas.

Easy idea

Replace the hasher with a faster hash, the default hash is dos resistant which we dont need since the MessageId's are purely internal.
This should actually be a pretty good win since we hash every incoming response

Implemented here #1486

Crazy Idea

• Replace MessageId with an incrementing u64, then rewrite the hashmap as a binary search over a VecDeque.
  • this avoids hashing all together
  • I suspect that insertion + removal for a hashmap is expensive, and this will completely avoid that.

However, before attempting any of this we should wait and see if hashmap insert/remove ever appears while profiling.