Java 25 support: drop the deprecated sun.misc.Unsafe path (jctools atomic queue)

[vasiliy-mikhailov]

Java 25 support: drop the deprecated sun.misc.Unsafe path

Resolves #775.

A plain jctools version bump does not fix it

The issue proposes bumping jctools to silence the terminally-deprecated
sun.misc.Unsafe warning on Java 25. I checked that directly, exercising the exact
queue this project uses (SpscUnboundedArrayQueue) on Temurin 25.0.3:

jctools	warning on Java 25
2.1.2 (current)	sun.misc.Unsafe::objectFieldOffset ⚠️
4.0.5	still sun.misc.Unsafe::objectFieldOffset ⚠️
4.0.5, atomic queue	clean ✅

jctools is built on Unsafe by design, so a newer version still trips the
warning.

The fix

jctools ships Unsafe-free *Atomic* queue variants (backed by
AtomicReferenceFieldUpdater) for exactly this situation. The only jctools usage
in the project is a single SPSC queue in MqttOutgoingQosHandler, so switching it
to org.jctools.queues.atomic.SpscUnboundedAtomicArrayQueue removes the Unsafe
code path entirely while keeping identical queue semantics:

-import org.jctools.queues.SpscUnboundedArrayQueue;
+import org.jctools.queues.atomic.SpscUnboundedAtomicArrayQueue;
...
-private final @NotNull SpscUnboundedArrayQueue<MqttPublishWithFlow> queue = new SpscUnboundedArrayQueue<>(32);
+private final @NotNull SpscUnboundedAtomicArrayQueue<MqttPublishWithFlow> queue = new SpscUnboundedAtomicArrayQueue<>(32);

The atomic variant uses field updaters rather than raw Unsafe offsets — a
negligible difference for this per-connection outgoing queue, and the idiomatic
jctools choice when Unsafe is unavailable or undesired. jctools is also bumped
2.1.2 → 4.0.5, as the issue requested.

Verification

• On Temurin 25.0.3, the atomic queue emits no sun.misc.Unsafe
  deprecation warning (the Unsafe-based queue does).
• Full ./gradlew test: 2619 passing / 12 skipped / 0 failures, identical
  before and after.
• ./gradlew assemble builds the shaded jar with the relocated atomic class.

Note: the build uses Gradle 8.14.3, which cannot itself run a Java 25 toolchain
(./gradlew test on JDK 25 fails to parse the version string). That's a separate,
build-only concern (needs Gradle ≥ 9); this PR addresses the library's runtime
Unsafe usage when consumed on Java 25.

🤖 Generated with Claude Code

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