feat: deterministic close on the wrappers that own native state

[milyin]

Implements the lifecycle policy from #518: a public wrapper exposes close() when it directly owns native state whose lifetime can escape the call.

ZBytes — discardable and closeable

ZBytes now implements AutoCloseable and exposes discard(). It needs no new state field — the two existing fields already encode every state, and eager == null && handle == null is "discarded":

state	discard()	later toBytes()
value (from(...))	no-op	bytes
received, unread	frees the native buffer	ZError
received, already materialized	no-op	bytes
discarded	no-op (idempotent)	ZError

discard() is @Synchronized on the same monitor as the lazy materialization, so read-vs-discard has two deterministic outcomes and never a use-after-free. The getter's handle!! became handle ?: throw ZError(...), so a read after discard is a clear closed-state error rather than an NPE — that covers toString/equals/hashCode/toZZBytes too, which all route through bytes. No Cleaner is added: the receive hot path is unchanged, and IntoZBytes is untouched.

Config — AutoCloseable

close() delegates to the generated handle's already-idempotent close(), keeping the Cleaner as the forgotten-close fallback. Zenoh.open uses zConfig.newClone(...) rather than consuming the config, so closing stays the user's decision; afterwards getJson/insertJson5/opening a session fail through the generated closed-handle guard as ZError. The class KDoc said the config was "consumed by open" — corrected.

SessionDeclaration : AutoCloseable

close() = undeclare() as a default. The six implementations (Publisher, Subscriber, Queryable, Querier, KeyExpr, LivelinessToken) already had exactly that override and keep it — this repo builds with Kotlin 1.9, where interface bodies compile to DefaultImpls, so leaving the per-class overrides in place is what keeps Java binary compatibility unconditional. The default is there for external/polymorphic use, as the issue asks.

Out of scope per the issue: Sample, Reply, Query, Encoding, and the Into* facades.

Tests

New ZBytesLifecycleTest.kt builds handle-backed instances directly (no session — the wrapper's state machine is what is under test) and covers: discard before materialization, discard after, repeated close()/discard(), a user-created ZBytes, and 500 rounds of concurrent read-vs-close asserting each read either returns the payload or throws ZError — nothing else. Plus one assertion that SessionDeclaration is AutoCloseable. ConfigTest gains a double-close/use-after-close test.

./gradlew :zenoh-java:test -PuseLocalFlatJni=true — 119 tests, all green (-PuseLocalFlatJni is needed because org.eclipse.zenoh:zenoh-flat-jni:1.9.0 is not on Maven yet).

Closes #518