refactor: asynchronous blob backing store (#10969)

Co-authored-by: Luca Casonato <hello@lcas.dev>

cli/tests/blob_gc_finalization.js

@@ -0,0 +1,11 @@
+// This test creates 1024 blobs of 128 MB each. This will only work if the blobs
+// and their backing data is GCed as expected.
+for (let i = 0; i < 1024; i++) {
+  // Create a 128MB byte array, and then a blob from it.
+  const buf = new Uint8Array(128 * 1024 * 1024);
+  new Blob([buf]);
+  // It is very important that there is a yield here, otherwise the finalizer
+  // for the blob is not called and the memory is not freed.
+  await new Promise((resolve) => setTimeout(resolve, 0));
+}
+console.log("GCed all blobs");