android(util): make FakeUnlockedCredential internal so callers can expose it

Internal var lastIssued: FakeUnlockedCredential still tripped the
exposed-private-type check because internal > private-in-file in
Kotlin's visibility ordering. Bump the class to internal — same
module-scope blast radius, fixes the property exposure cleanly.

Author: pulkitpareek18

android/app/src/main/java/dev/zeroauth/android/util/FakeProverAndSec.kt

@@ -41,7 +41,12 @@ import kotlinx.coroutines.delay
 
 // ─── Fake credential ─────────────────────────────────────────────
 
-private class FakeUnlockedCredential(
+// Internal (not private-in-file) so the `FakeKeystoreManager.lastIssued`
+// property below — also internal — can expose it without tripping
+// kotlinc's E_EXPOSED_PROPERTY_TYPE check. The class still doesn't
+// leak outside the module; the production prover and tests are the
+// only callers.
+internal class FakeUnlockedCredential(
     override val biometricSecret: String,
     override val salt: String,
     override val commitment: String,