Fix fetched Headers methods under @types/node

[KayleeWilliams]

I hit this moving our CLI (inthhq/inth) to 0.2. Our HTTP client reads headers off fetch responses, and with @types/node installed it crashes:

const res = await fetch(url);
res.headers.get("x-request-id");
// TypeError: res.headers.get is not a function

It works on 0.1.7, and without @types/node. undici-types declares Headers methods as properties (readonly get: (name: string) => string | null), so lower-calls.ts reads get off the native handle and calls the result. The handle only answers get as a method, so the read comes back undefined.

This sends members declared by the standard library or @types/node back through dynInvoke, like 0.1.7 did. Callback properties in user code still go through read-then-call.

The new node-types test fetches from a local server and compares with Node. It fails on main and passes with this. The corpus and the fetch tests pass otherwise, except 1640-fd-read-decode.ts, 2283-structured-clone.cjs, stream-from-immediate-cancel, static and static-stream-this, which fail on main for me too (Node 24.19). I didn't run the sanitized lane.

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