feat(data-rpc): schema-driven bidirectional service projection across iframe/MessagePort

[krisnye]

Description

New @adobe/data-rpc package: schema-driven, bidirectional projection of
@adobe/data async data services across a boundary (iframe / MessagePort /
Worker). One createRpcEndpoint(transport) per side; each can expose its own
services and consume the peer's over a single channel.

Core invariant: only Data ever crosses the wire. We never serialize an
Observe/Promise/AsyncGenerator/function — the consuming side synthesizes an
equivalent-shaped service locally whose members translate to/from Data-only
messages. Gating expose on AsyncDataService.IsValidWithCompleteSchema
guarantees there is nothing but Data to marshal.

Highlights:

• All five member kinds: Observe, fn:observe, fn:promise, fn:generator
  (strictly pull-based), fn:void.
• Nested sub-services shimmed recursively to any depth; members addressed by
  path from the service root.
• Constructor-typed arguments (reverse channel): an Observe, Promise, or
  AsyncGenerator passed as/inside a call argument is serviced from the caller —
  the caller sends a ref and the value is streamed/settled/pulled back over a
  reverse channel; only Data crosses.
• Transports: createMessagePortTransport (primary), createWindowTransport
  (port handoff + origin allowlist), createRpcLoopbackTransport (tests).
• Errors marshaled as {name,message,stack}; separate per-originator id tables;
  graceful close teardown (pending calls reject, subscriptions/generators end).
• Trust v1: transport-level (origin allowlist + only exposed services) + a
  canInvoke seam + incoming arg validation against signature.parameters.

Also:

• Extracts the shared memberKind classifier out of create-lazy.ts into
  async-data-service/member-kind.ts (re-exported via AsyncDataService);
  createLazy behavior unchanged.
• Adds data-rpc-iframe — a Lit sample (main frame + real iframe over a
  MessagePort) demonstrating all four kinds in both directions plus a nested
  sub-service.

Test evidence

• 48 unit tests in @adobe/data-rpc (every member kind both directions; hard
  paths: close-mid-call, unsubscribe-in-flight, generator early return/dispose,
  bidirectional id independence, consume-before-expose, arg-validation rejection,
  teardown-on-close; nested services and Observe/Promise/AsyncGenerator arguments
  over loopback and a real MessageChannel).
• @adobe/data service suite (122 tests) still green after the memberKind extract.
• Sample integration test + live browser verification: all four kinds and the
  nested sub.calc.* sub-service confirmed working across the iframe, console clean.
• Full monorepo pnpm run lint + pnpm run typecheck pass (caches cleared).

Related PRs

Builds on #196 (pure-JSON Schema + observable Service.schema slot).

Jira ticket

N/A — no ticket (public repo, library feature).