Parallelize singleton execution

Bug: 281536768
Test: manual, presubmits
Change-Id: I57fdc76ba6b277e88e196b506af87127a530fd37
diff --git a/rust/rust.go b/rust/rust.go
index dc53cc0..4324ecb 100644
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -45,7 +45,7 @@
 	})
 	pctx.Import("android/soong/rust/config")
 	pctx.ImportAs("cc_config", "android/soong/cc/config")
-	android.InitRegistrationContext.RegisterSingletonType("kythe_rust_extract", kytheExtractRustFactory)
+	android.InitRegistrationContext.RegisterParallelSingletonType("kythe_rust_extract", kytheExtractRustFactory)
 }
 
 type Flags struct {