Proposal: build the protocol worker without the type checker (split monty-proto's `worker` feature)

We embed Monty's protocol worker in a WASI host: wazero, from Go. It runs sandboxed Python transforms on each request in an LLM API gateway. We drive monty-proto's worker::Child over the framed monty.v1 protocol and always feed with skip_type_check, so the type checker is never used. But it can't be left out of the build: monty-proto's worker feature is

worker = ["dep:monty", "dep:monty-type-checking", "monty-types/tzdb-bundled"]

so every worker links ty, ruff_db, salsa and the typeshed stubs. monty-wasm-runtime depends on monty-proto with worker as well, so the JS worker carries the checker too.

What it costs, measured at 1.3.0 (ca1b75be), wasm32-wasip1 release, same stack size:

Runtime behaviour was otherwise unchanged in our tests: limits, per-call latency, and all feeds with skip_type_check. To get these numbers we replaced monty-type-checking in the workspace with an API-compatible stub. It provides SourceFile, TypeCheckContext, TypeChecker and scan_imports, and its run_with returns an error. Those four items are all worker.rs uses.

Proposal (non-breaking):

worker-core = ["dep:monty", "monty-types/tzdb-bundled"]
worker = ["worker-core", "dep:monty-type-checking"]

• Gate the type-checking paths in worker.rs on the checker being present: the TypeChecker field, type_check_feed, the scan_imports call, and the reset call.
• When a worker built without it receives Configure { type_check: true, .. }, reject it with a clear error, for example "type checking is not built into this worker".
• Existing users of worker see no change. Embedders that never type-check can depend on worker-core.

Thanks for #1113, by the way: we hit the same 32-bit HeapData size assertion when the checker's dependency tree was the only thing turning on smallvec/union.

Happy to send a PR for this if the approach looks right to you.