Add @immutable annotations to VerificationResult and its subclasses.

This change marks the VerificationResult sealed interface and all its concrete data classes as immutable. Suppressions are added for types like PublicKey and Exception, which are effectively immutable for the purposes of this class but not formally annotated as such.

PiperOrigin-RevId: 855770774

Author: agxp

src/main/kotlin/Verifier.kt

@@ -23,6 +23,7 @@ import com.android.keyattestation.verifier.provider.ProvisioningMethod
 import com.android.keyattestation.verifier.provider.RevocationChecker
 import com.google.common.collect.ImmutableList
 import com.google.common.util.concurrent.ListenableFuture
+import com.google.errorprone.annotations.Immutable
 import com.google.errorprone.annotations.ThreadSafe
 import com.google.protobuf.ByteString
 import com.google.protobuf.kotlin.toByteString
@@ -42,8 +43,13 @@ import kotlinx.coroutines.guava.future
 import kotlinx.coroutines.runBlocking
 
 /** The result of verifying an Android Key Attestation certificate chain. */
+@Immutable
 sealed interface VerificationResult {
+  @Immutable
   data class Success(
+    @SuppressWarnings(
+      "Immutable"
+    ) // PublicKey implementations are immutable but not marked as such.
     val publicKey: PublicKey,
     val challenge: ByteString,
     val securityLevel: SecurityLevel,
@@ -52,18 +58,31 @@ sealed interface VerificationResult {
     val attestedDeviceIds: DeviceIdentity,
   ) : VerificationResult
 
-  data object ChallengeMismatch : VerificationResult
+  @Immutable data object ChallengeMismatch : VerificationResult
 
-  data class PathValidationFailure(val cause: CertPathValidatorException) : VerificationResult
+  @Immutable
+  data class PathValidationFailure(
+    @SuppressWarnings("Immutable") // Exceptions are not deeply immutable.
+    val cause: CertPathValidatorException
+  ) : VerificationResult
 
-  data class ChainParsingFailure(val cause: Exception) : VerificationResult
+  @Immutable
+  data class ChainParsingFailure(
+    @SuppressWarnings("Immutable") // Exceptions are not deeply immutable.
+    val cause: Exception
+  ) : VerificationResult
 
-  data class ExtensionParsingFailure(val cause: ExtensionParsingException) : VerificationResult
+  @Immutable
+  data class ExtensionParsingFailure(
+    @SuppressWarnings("Immutable") // Exceptions are not deeply immutable.
+    val cause: ExtensionParsingException
+  ) : VerificationResult
 
+  @Immutable
   data class ExtensionConstraintViolation(val cause: String, val reason: KeyAttestationReason) :
     VerificationResult
 
-  data object SoftwareAttestationUnsupported : VerificationResult
+  @Immutable data object SoftwareAttestationUnsupported : VerificationResult
 }
 
 /**