Build with mls_build_async

This switches the API to use async Rust throughout. We need async APIs
for the Jetpack library.

Bug: 337838209
Test: Presubmit
Change-Id: Ia00ed78a416839f3e3087524f557fe5e5ccf4d7c
diff --git a/Android.bp b/Android.bp
index 41c31d8..d32e137 100644
--- a/Android.bp
+++ b/Android.bp
@@ -31,6 +31,7 @@
         "preallocate",
         "std",
     ],
+    cfgs: ["mls_build_async"],
     rustlibs: ["libthiserror"],
     proc_macros: ["libmls_rs_codec_derive"],
     apex_available: [
diff --git a/cargo_embargo.json b/cargo_embargo.json
index cb908d7..d0bed4a 100644
--- a/cargo_embargo.json
+++ b/cargo_embargo.json
@@ -1,3 +1,4 @@
 {
-  "run_cargo": false
+  "run_cargo": false,
+  "extra_cfg": ["mls_build_async"]
 }