refactor(npm): improve locking around updating npm resolution (#24104)

Introduces a `SyncReadAsyncWriteLock` to make it harder to write to the
npm resolution without first waiting async in a queue. For the npm
resolution, reading synchronously is fine, but when updating, someone
should wait async, clone the data, then write the data at the end back.

cli/util/sync/async_flag.rs

@@ -0,0 +1,20 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+use tokio_util::sync::CancellationToken;
+
+#[derive(Debug, Default, Clone)]
+pub struct AsyncFlag(CancellationToken);
+
+impl AsyncFlag {
+  pub fn raise(&self) {
+    self.0.cancel();
+  }
+
+  pub fn is_raised(&self) -> bool {
+    self.0.is_cancelled()
+  }
+
+  pub fn wait_raised(&self) -> impl std::future::Future<Output = ()> + '_ {
+    self.0.cancelled()
+  }
+}