Switch CreateWorktreeResponse::worktree_id to be a i32

Apparently all IDs in `sqlx` on the server are represented as i32s.

zed-rpc/src/rest.rs

@@ -2,6 +2,6 @@ use serde::{Deserialize, Serialize};
 
 #[derive(Serialize, Deserialize)]
 pub struct CreateWorktreeResponse {
-    pub worktree_id: u64,
+    pub worktree_id: i32,
     pub rpc_address: String,
 }