Conformance: in-suite QUIC cases (in-memory noq loopback, RFC 9001 vectors on every target)

[lann]

Follow-up to the conformance cutover, which covers the TLS record path through the composed component. The QUIC layer's conformance-worthy behavior should also run per target through the suite:

• RFC 9001 known answers (initial keys, ChaCha20 short-header protection, key update, retry integrity) currently run only as native cargo test on the host — never inside a wasm engine. As suite cases they run on every target, which is the point once jco targets exist (Conformance: jco targets blocked on upstream jco defects in composed p3 stream/future paths #28's fix lands V8's JIT under the same vectors as wasmtime's Cranelift): the profile's timing story is per-runtime-empirical, and so is its correctness story.
• An in-memory noq loopback (two noq-proto endpoints under polymorph-tls-quic, datagrams exchanged through in-suite queues — no wasi:sockets, so the cases stay browser-compatible) covering handshake, bidirectional streams, and clean close.

These cases link polymorph-tls-quic into the suite rather than crossing the WIT surface — the value is engine coverage of the pure-wasm crypto stack, not composition coverage. Vector data should move (not copy) out of the native tests to avoid a drifting duplicate; unit-shaped tests of internal APIs stay put.

examples/quic-loopback (QUIC over real wasi:sockets UDP under wasmtime) stays as the transport-integration rig either way; the suite cases replace none of it.

[lann]

Still open and now unblocked on the target side. The jco reference is stale — #28 is closed and the jco legs were retired in #42 — but the condition it was waiting on is now satisfied by the deltic legs: stock Deno (#36) and headless Chromium (#39) put V8 rows in the matrix, so the per-engine rationale for running the RFC 9001 vectors as suite cases is live today rather than contingent. Current state on main: the suite (conformance/guest-ct) has no QUIC cases and no polymorph-tls-quic linkage, and the vectors run native-only in rust/quic/src/packet.rs. One sequencing note: the vector move should coordinate with #11's remaining scope (upstreaming packet.rs to rustls-rustcrypto), so the vectors end up in the suite here and in unit tests upstream, rather than duplicated or orphaned.