util: Add function to check for Android sparse image magic

src/util/sparse.ts

@@ -0,0 +1,15 @@
+import { promises as fs } from 'fs'
+
+const FILE_MAGIC = 0xed26ff3a
+
+export async function isSparseImage(path: string) {
+  let file = await fs.open(path, 'r')
+  try {
+    let buf = new Uint32Array(1)
+    await file.read(buf, 0, 4)
+
+    return buf[0] == FILE_MAGIC
+  } finally {
+    await file.close()
+  }
+}