Fix ASAN crash in shell rm builtin due to race condition

Fixed a use-after-free bug in the rm builtin caused by inadequate memory
synchronization between threads. The issue occurred when child tasks finished
and triggered parent task cleanup while the parent was still being accessed.

Changes:
- Changed memory ordering from .monotonic to .seq_cst in enqueueNoJoin() to
  ensure subtask_count increments are immediately visible to all threads
- Changed memory ordering from .monotonic to .acquire when loading need_to_wait
  to properly synchronize with the .seq_cst store
- Fixed memory leak when deleteAfterWaitingForChildren() enqueues new children
  by resetting deleting_after_waiting_for_children and need_to_wait flags so
  that cleanup can proceed when those children finish

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/shell/builtin/rm.zig

@@ -610,7 +610,7 @@ pub const ShellRmTask = struct {
                     // It's possible that we queued this subdir task and it finished, while the parent
                     // was still in the `removeEntryDir` function
                     const tasks_left_before_decrement = this.parent_task.?.subtask_count.fetchSub(1, .seq_cst);
-                    const parent_still_in_remove_entry_dir = !this.parent_task.?.need_to_wait.load(.monotonic);
+                    const parent_still_in_remove_entry_dir = !this.parent_task.?.need_to_wait.load(.acquire);
                     if (!parent_still_in_remove_entry_dir and tasks_left_before_decrement == 2) {
                         this.parent_task.?.deleteAfterWaitingForChildren();
                     }
@@ -650,6 +650,10 @@ pub const ShellRmTask = struct {
                 },
                 .result => |deleted| {
                     if (!deleted) {
+                        // New children were enqueued, so we need to wait for them
+                        // Reset the flag so that when those children finish, they can properly clean up
+                        this.deleting_after_waiting_for_children.store(false, .seq_cst);
+                        this.need_to_wait.store(true, .release);
                         do_post_run = false;
                     }
                 },
@@ -739,7 +743,7 @@ pub const ShellRmTask = struct {
             .concurrent_task = jsc.EventLoopTask.fromEventLoop(this.event_loop),
         };
 
-        const count = parent_task.subtask_count.fetchAdd(1, .monotonic);
+        const count = parent_task.subtask_count.fetchAdd(1, .seq_cst);
         if (comptime bun.Environment.allow_assert) {
             assert(count > 0);
         }