fix(cognito): keep revoked tokens across restarts

RevokedTokenInfo serialized its derived isExpired() as "expired", which the
persistent store's ObjectMapper then refused to read back. On restart the file
was moved aside as .corrupt and every revocation was forgotten, so refresh
tokens revoked by sign-out worked again. The derived field is no longer
written, and files that carry it are read with it ignored.

src/test/java/io/github/hectorvent/floci/services/cognito/RevokedTokenInfoPersistenceTest.java

@@ -0,0 +1,44 @@
+package io.github.hectorvent.floci.services.cognito;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.services.cognito.model.RevokedTokenInfo;
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+/** Revoked tokens must survive a restart, which reads them back with a strict ObjectMapper. */
+class RevokedTokenInfoPersistenceTest {
+
+    private static final TypeReference<Map<String, RevokedTokenInfo>> TYPE = new TypeReference<>() {
+    };
+    private final ObjectMapper strictMapper = new ObjectMapper();
+
+    @Test
+    void roundTripsWithoutTheDerivedExpiredField() throws Exception {
+        RevokedTokenInfo info = new RevokedTokenInfo("jti-1", "refresh", "alice", "us-east-1_pool", 1_000L, 4_102_444_800L);
+
+        String json = strictMapper.writeValueAsString(Map.of("k", info));
+        RevokedTokenInfo read = strictMapper.readValue(json, TYPE).get("k");
+
+        assertFalse(json.contains("\"expired\""), json);
+        assertEquals("jti-1", read.getJti());
+        assertEquals(4_102_444_800L, read.getExpiresAt());
+    }
+
+    @Test
+    void readsFilesWrittenWithTheExpiredField() throws Exception {
+        String saved = """
+                {"000000000000/revoked:us-east-1_pool:jti-1":{"jti":"jti-1","tokenType":"refresh","username":"alice",
+                 "userPoolId":"us-east-1_pool","revokedAt":1792858112669,"expiresAt":1824394112,"expired":false}}
+                """;
+
+        RevokedTokenInfo read = strictMapper.readValue(saved, TYPE).get("000000000000/revoked:us-east-1_pool:jti-1");
+
+        assertEquals("alice", read.getUsername());
+        assertEquals(1824394112L, read.getExpiresAt());
+    }
+}