fix(core): Imposter.uri() reports the admin host, not the host the imposter is bound to

[EtaCassiopeia]

Closes #243

The engine binds an imposter on its own host, defaulting to 0.0.0.0 (IPv4 only), whatever interface the admin API uses (crates/rift-mock-core/src/imposter/manager.rs:836). Imposter.uri() always reported the admin host. So an imposter bound elsewhere was unreachable at its uri(), and so was a default imposter behind an IPv6 admin host. Found by #232's live IT.

Changes

• RiftImpl records whether the SDK runs the engine itself: spawned and embedded do, connect doesn't. testcontainers goes through connect, so it keeps its gateway resolver.
  • For a connected engine, an imposter's bind host is an address on another machine, so the resolver stays in charge.
  • A user-supplied hostResolver can't be set on spawn or embedded anyway: both build their ConnectOptions internally.
• Where the host comes from:
  • create reads it from the JSON the SDK posted. The engine's create response doesn't echo it.
  • imposter(port) and imposters() on a local engine read the replayable list. The engine's single-imposter GET never includes host, and neither does the non-replayable list. This was caught in review. The cost is one replayable list per lookup on a local engine. A connected engine is unchanged.
• ImposterImpl.uri() uses HostAuthority.httpUri(host, port) for a concrete host. Any spelling of the wildcard (0.0.0.0, ::, [::], 0:0:0:0:0:0:0:0) falls back to the resolver, as does an absent host.
• Docs: Javadoc on Imposter.uri() states the rule. It also says to set ImposterSpec.host("::1") when the admin host is IPv6, since a host-less imposter is IPv4-only.

Tests

• ImposterUriHostTest (4):
  • a concrete host wins on spawned and embedded engines (IPv4, ::1, [::1], localhost);
  • every wildcard spelling, and an absent host, falls back to the admin host;
  • lookups read the replayable list;
  • an unknown port is empty.
• RemoteTransportCoverageTest: a connected engine keeps its resolver whatever host the imposter names.
• Live Ipv6HostIT, new case on a default spawned engine (admin 127.0.0.1) with an imposter on ::1:
  • uri(), imposter(port).uri() and imposters().get(0).uri() all report [::1], and a GET succeeds.
  • With the local-engine flag forced off, the same case fails with 127.0.0.1.
  • The existing spawn and embedded cases still pass. Embedded was run on JDK 25 with the 0.18.0 dylib.
• ./mvnw verify passes on all modules.
• The full spawn conformance IT suite passes locally, apart from three tests that need the downloaded corpus and one that asserts the engine version against a local dev binary. CI provides both.

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