Fix clippy warnings across workspace

- io.rs: factor the pending-RPC-replies map into a PendingReplies
  type alias (type_complexity)
- lua_env.rs: drop a redundant i64->i64 cast and an unneeded borrow
  before create_string (unnecessary_cast, needless_borrows_for_generic_args)
- state_engine.rs: iterate watches.values() instead of discarding the
  key from watches.iter() (for_kv_map)
- module_host_sandbox.rs: collapse nested if into a single condition
  (collapsible_if)

(cherry picked from commit 49063cb98ddfeae35d842a6cf439123cfda763d9)

breadd/src/core/state_engine.rs

@@ -260,7 +260,7 @@ pub async fn run_state_engine(
                 }
 
                 if let (Some(before), Some(after)) = (before_snapshot, after_snapshot) {
-                    for (_id, path) in watches.iter() {
+                    for path in watches.values() {
                         let old_val = value_at_path(&before, path).unwrap_or(Value::Null);
                         let new_val = value_at_path(&after, path).unwrap_or(Value::Null);
                         if old_val != new_val {