Ergonomic announced streams in Swift and Kotlin wrappers

[kixelated]

Summary

The announced subscription was awkward to consume in the language wrappers: you acquired a handle and then called a separate stream member whose name stuttered against the handle (announced.announcements() / announced.announcements). This reworks the Swift and Kotlin wrappers so each stream reads idiomatically in its own language. moq-ffi is untouched on purpose. uniffi can't carry a stream across the FFI boundary, so the pull-based next() handle is the only option and the ergonomics belong in the wrappers (Python already does this).

• Swift: MoqAnnounced now conforms to AsyncSequence, so the handle iterates directly:

  for try await announcement in announced { ... }

• Kotlin: replaced the stuttering MoqAnnounced.announcements() extension with a fused MoqOriginConsumer.announcements(prefix): Flow that acquires the subscription on first collection and cancels it via try/finally (forwarding cancellation on every completion path, not just CancellationException):

  consumer.announcements("demos/").collect { announcement -> ... }

  This matches how the other consumers already pair a low-level next() with a Flow extension.

Docs and per-language READMEs are updated to the new call sites.

Go deferred

Go was dropped from this PR. Its bindings have no ergonomic layer at all (every stream is raw), and bringing it to parity is entangled with a larger open question: whether the compiled-FFI wrappers (Swift/Kotlin/Go) should move to a Python-style hand-written wrapper layer, and whether to drop the moq.MoqClient stutter. That's a deliberate, separately-scoped refactor rather than a rider on this announced-ergonomics change.

Why dev

This is a breaking change to the public Swift/Kotlin wrapper APIs (the old .announcements member is gone), which per the branch-targeting rule belongs on dev. It also builds naturally on the auto-origin session rework already on dev (cs.consumer() etc.), which the updated docs use.

Design note for reviewers

Teardown-on-abandon differs slightly between the two, pre-existing and left as-is: Swift cancels on any stream termination; Kotlin cancels on coroutine cancellation (the new fused announcements also cancels the handle it acquired via try/finally).

Test plan

• Swift: just swift builds + smoke tests pass, no @retroactive/conformance warnings.
• Kotlin: signatures verified against generated bindings, but Gradle wasn't available locally for a full just kt check.

(Written by Claude)