Clean up imports, formatting and tests.

Bug: n/a
Test: atest libapkverify.test libapkverify.integration_test
Change-Id: I39686d17927741297aa3feb02ed6043ee770933b
diff --git a/apkverify/src/lib.rs b/apkverify/src/lib.rs
index 869431e..f75913c 100644
--- a/apkverify/src/lib.rs
+++ b/apkverify/src/lib.rs
@@ -18,7 +18,8 @@
 
 mod bytes_ext;
 mod sigutil;
-mod testing;
+#[allow(dead_code)]
+pub mod testing;
 mod v3;
 mod ziputil;