Move ProtoClient to RPC crate, behind feature flag disabled in collab (#17908)

This fixes a bug where we accidentally added a `gpui` transitive
dependency in `collab`.

Release Notes:

- N/A

crates/project/src/worktree_store.rs

@@ -17,8 +17,8 @@ use gpui::{
 };
 use postage::oneshot;
 use rpc::{
-    proto::{self, AnyProtoClient, SSH_PROJECT_ID},
-    TypedEnvelope,
+    proto::{self, SSH_PROJECT_ID},
+    AnyProtoClient, TypedEnvelope,
 };
 use smol::{
     channel::{Receiver, Sender},