fix(ext/web): structuredClone of non-serializable Web types throws DataCloneError

[fibibot]

Summary

structuredClone(new Response()) (and the same with Request, Headers, ReadableStream, WritableStream, TransformStream) silently produced an empty {} instead of throwing DataCloneError like Node and the Web Platform spec require:

$ deno run repro.cjs
structuredClone succeeded unexpectedly: {}
$ node repro.cjs
structuredClone threw: DataCloneError Cannot clone object of unsupported type.

These types have no enumerable own properties — they're effectively branded JS objects whose state lives in internal slots. V8's ValueSerializer doesn't know they're "platform" types, so it treats them as ordinary objects with no entries to serialise, and the fast core.structuredClone(value) path returns {}.

Pre-check the input against a lazily-resolved list of known non-serializable Web globals before handing off to V8. Each prototype is looked up at first call (so the fix doesn't depend on bootstrap ordering / wouldn't introduce circular ext imports between web and fetch), then ObjectPrototypeIsPrototypeOf is used for the brand check.

The list:

• Headers, Request, Response — explicitly not [Serializable] per Fetch §2.2.5 / §6 / §7.
• ReadableStream, WritableStream, TransformStream — [Transferable] (only via the transfer list), not [Serializable].

Fixes #32914.

Test plan

• Added tests/specs/run/structured_clone_non_serializable covering each non-serializable type plus positive controls (plain object / array / Date) to confirm valid types still clone.
• Manually re-ran the issue's reproducer; before this PR prints structuredClone succeeded unexpectedly: {}, after prints structuredClone threw: DataCloneError Cannot clone object of unsupported type. (matches Node).
• ./x fmt clean.
• ./x lint clean (full Rust + JS).

[bartlomieju]

Nice fix! Two observations:

Nested objects are not caught. The check only inspects the root value, so structuredClone({ nested: new Response() }) will still silently produce { nested: {} }. Node/browsers catch this at any depth because V8's C++ ValueSerializer::Delegate::ThrowDataCloneError fires during traversal. Inherently hard to fix from JS-land, but worth noting as a known remaining gap (maybe a comment or a follow-up issue).

Missing test coverage for WritableStream / TransformStream. They're marked with markNotSerializable but the test only covers ReadableStream. Worth adding two more check() lines.