Use RpcSend on RPC::self_limiter::ready_requests

[jxs]

Issue Addressed

We don't need to store BehaviourAction for ready_requests and therefore avoid having an unreachable! on #6625.
Therefore this PR should be merged before it

[ackintosh]

Thanks for this @jxs! This is helpful for simplifying #6625, but do we still need unreachable! on #6625 like this?:

                if let RPCSend::Request(request_id, req) = event {
                    //
                } else {
                    unreachable!()
                }

[jxs]

Thanks for this @jxs! This is helpful for simplifying #6625, but do we still need unreachable! on #6625 like this?:

                if let RPCSend::Request(request_id, req) = event {
                    //
                } else {
                    unreachable!()
                }

we can just return false on that situation right? (same as before true)

[ackintosh]

It will look like this if we return false instead of unreachable! on #6625:

    pub fn peer_disconnected(&mut self, peer_id: PeerId) -> Vec<(Id, Protocol)> {
        // ...

        self.ready_requests.retain(|(req_peer_id, event)| {
            if let RPCSend::Request(request_id, req) = event {
                if req_peer_id == &peer_id {
                    failed_requests.push((*request_id, req.protocol()));
                    // Remove the entry
                    false
                } else {
                    // Keep the entry
                    true
                }
            } else {
                // unreachable!()

                // Remove the unexpected RPCSend variant 
                false
            }
        });

We can do that, but I think unreachable! is more appropriate in this situation to clearly indicate that the else clause is unreachable.

[mergify]

This pull request has been removed from the queue for the following reason: checks failed.

The merge conditions cannot be satisfied due to failing checks:

• ☑️ local-testnet-success

You should look at the reason for the failure and decide if the pull request needs to be fixed or if you want to requeue it.

If you want to requeue this pull request, you need to post a comment with the text: @mergifyio requeue

[mergify]

This pull request has been removed from the queue for the following reason: checks failed.

The merge conditions cannot be satisfied due to failing checks:

• ☑️ test-suite-success

You should look at the reason for the failure and decide if the pull request needs to be fixed or if you want to requeue it.

If you want to requeue this pull request, you need to post a comment with the text: @mergifyio requeue