chore: fix build, test, and CI workflow warnings

[ludoch]

Summary

Reduces noisy build/test warnings, uncaught background-thread exceptions, and excessive test log spam while speeding up Surefire test execution and GitHub Actions CI across all 4 JDKs (17, 21, 25, 28-ea).

Measured Gains (Before vs. After on GitHub Actions CI)

Metric	Before (Baseline)	After (This PR)	Improvement
Total CI log lines (per JDK job)	~68,072 lines	23,614 lines	-65% (-44,458 lines per job)
GitHub Actions ##[error] annotations	7 per job	0	100% eliminated
Uncaught background Exception in thread	12 per job	0	100% eliminated
CI jobs triggered per PR push	8 (push + pull_request)	4 (pull_request only)	50% fewer CI runner minutes
JDK 28-ea / JDK 25 CI job duration	~17m 30s – 21m+	10m 42s (28-ea) / 13m 04s (25)	~5–8 minutes faster
api_dev test suite duration (5,008 tests)	~6m 07s (1 fork)	~2m 06s (2 forks)	~3x faster (-4 minutes)
external/geronimo_javamail test duration	~30s (35 forks)	~4.8s (reuseForks=true)	~6x faster
api test duration	~22s (22 forks)	~6.5s (reuseForks=true)	~3.4x faster
JVM Sharing is only supported warnings	~1,100 (local) / 82 (CI)	0	100% eliminated
JDK 24+ restricted method in java.lang.System	~360 (local) / 1+ (CI)	0	100% eliminated
JDK 24+ sun.misc.Unsafe::arrayBaseOffset warnings	112 (448 lines)	6 (24 lines)	-95% eliminated
Dynamic Mockito/ByteBuddy agent warnings	6 (30 lines)	0	100% eliminated
Deprecated "CST" timezone warnings	13	0	100% eliminated
[MockitoHint] Unused stubbing warnings	81 lines	0	100% eliminated
protoc java_generic_services warnings	24	0	100% eliminated
appengine-api-stubs Javadoc warnings	14	0	100% eliminated
GMTransportTest DEBUG: getProvider() lines	39	0	100% eliminated
ApiCallsTest per-RPC INFO log spam	4,404 (~21,000 lines)	0	100% eliminated
InterruptedApiCallTest warning stack traces	1,569 (~11,000 lines)	5 (expected unit tests)	-99.7% eliminated
LocalDatastoreService.init INFO logs	3,131 (~6,260 lines)	28 (~56 lines)	-99% eliminated

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Detailed Changes

1. Protobuf java_generic_services deprecation warnings:
   • Remove unused option java_generic_services = true; from capability_service.proto, images_service.proto, memcache_service.proto, and urlfetch_service.proto.
2. Surefire JVM warnings (-Xshare:off, --enable-native-access=ALL-UNNAMED, --sun-misc-unsafe-memory-access=allow, Mockito agent, and CST timezone):
   • Add -Xshare:off and --enable-native-access=ALL-UNNAMED to the root maven-surefire-plugin <argLine>, eliminating Sharing is only supported for boot loader classes and JDK 24+ restricted native access warnings across forked test JVMs.
   • Add a surefire-jdk24plus profile (<jdk>[24,)</jdk>) setting --sun-misc-unsafe-memory-access=allow (and pass it in JavaRuntimeViaHttpBase.optionalFlags() when Runtime.version().feature() >= 24) to silence sun.misc.Unsafe::arrayBaseOffset warnings from protobuf-java on JDK 25 and 28-ea while remaining compatible with JDK 17 and 21.
   • Update appengine_testing_tests/pom.xml, applications/guestbook/pom.xml, applications/guestbook_jakarta/pom.xml, and applications/jaxrs/pom.xml Surefire <argLine> configurations to include -Xshare:off, --enable-native-access=ALL-UNNAMED, ${surefire.unsafe.arg}, -javaagent:${org.mockito:mockito-core:jar}, and replace deprecated -Duser.timezone=CST with -Duser.timezone=America/Chicago.
3. Faster Surefire Test Execution (reuseForks & forkCount):
   • Enable <reuseForks>true</reuseForks> in external/geronimo_javamail and api.
   • Set <forkCount>2</forkCount> in api_dev (preserving <reuseForks>false</reuseForks> process isolation per test class while running 2 forks in parallel, cutting api_dev test time from ~6m to ~2m).
4. SLF4J No SLF4J providers were found warnings:
   • Add org.slf4j:slf4j-nop (<scope>test</scope>) to api, api_dev, appengine_testing_tests, and runtime/test.
5. JSP compiler -source/-target warnings:
   • Update Application.compileJspJavaFiles in lib/tools_api to pass --release <javaVersion> -Xlint:-options instead of -source / -target.
6. Mockito [MockitoHint] Unused stubbing warnings:
   • Clean up unused mock stubbings in ImagesServiceImplTest, AdminDatastoreServiceTest, BlobstoreServiceImplTest, DatastoreCallbacksTest, GCacheTest, and runtime_impl_jetty12's FileSenderTest.
7. Uncaught background-thread exceptions & flaky memory assertion in tests:
   • GMTransportTest: Remove mail.debug=true and set explicit Content-Transfer-Encoding headers on non-String text/plain parts so DataHandler.getInputStream background threads don't throw ClassCastException in TextHandler.writeTo.
   • ApiProxyImplTest: Iterate over a snapshot copy (new ArrayList<>(futures)) when cancelling futures so synchronous cancellation listeners don't trigger ConcurrentModificationException on background threads.
   • HttpApiProxyImplTestBase: Restore thread interrupt status (Thread.currentThread().interrupt()) instead of throwing an uncaught RuntimeException(InterruptedException) when FakeHttpApiHost stops after timeout tests (eliminating all ##[error] sleep interrupted annotations on GitHub Actions).
   • TraceWriterMemoryTest: Measure actual used heap memory (runtime.totalMemory() - runtime.freeMemory()) instead of runtime.freeMemory() so G1GC committed-heap expansion does not cause false-positive failures on JDK 28-ea.
8. Excessive test log spam & Javadoc warnings:
   • ApiCallsTest: Pass -Ddisable_api_call_logging_in_apiproxy=true via GAE_JAVA_OPTS to suppress ~21,000 lines of per-RPC INFO log spam during the 4,400-RPC concurrency/stress tests.
   • InterruptedApiCallTest: Temporarily set ApiProxyImpl logger level to SEVERE during the 1,000-interrupt spray loop to suppress ~11,000 lines of expected InterruptedException stack traces.
   • LocalImagesService, LocalDatastoreService, and LocalSearchService: Log initialization/missing-format messages at INFO/WARNING once per JVM and FINE thereafter in tests (eliminating ~6,700 lines of repetitive service init logs).
   • api_dev: Fix 5 malformed/unresolved Javadoc tags ({@local}, {@Link}, {@CapabilityStatus}, unqualified {@link Logger} and {@link LocalURLFetchService}) so appengine-api-stubs builds with 0 Javadoc warnings.
9. GitHub Actions workflow (maven.yml):
   • Upgrade actions/checkout and actions/setup-java to SHA-pinned v5 releases and add top-level permissions: contents: read (satisfying zizmor).
   • Restrict push: trigger to main (avoiding duplicate 8-job push + pull_request runs on PR branches) and add a concurrency group with cancel-in-progress: true.