feat(core): add cloneable resource registry for structured clone support

Adds infrastructure for custom JS objects to support structured cloning
via `postMessage`/`MessageChannel`. This enables objects like
`CryptoKey` and `X509Certificate` to be cloned across message ports.

The mechanism works by:
1. Objects set `[core.hostObjectBrand]` to a serializer function that
   returns `{ type: "<name>", ...data }`
2. Extensions register a deserializer via
   `core.registerCloneableResource(name, deserializerFn)`
3. During deserialization, the registry is consulted to reconstruct
   the original object

Changes:
- `libs/core/01_core.js`: Add `registerCloneableResource` /
  `getCloneableDeserializers` registry, auto-pass deserializers
  in `structuredClone`
- `libs/core/ops_builtin_v8.rs`: Mark `op_deserialize` as reentrant
  so deserializer callbacks can invoke ops
- `ext/web/13_message_port.js`: Pass cloneable deserializers during
  message deserialization

Ref: #12067
Ref: #12734

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bartlomieju

ext/web/13_message_port.js

@@ -409,6 +409,12 @@ function deserializeJsMessageData(messageData) {
     };
   }
 
+  const deserializers = core.getCloneableDeserializers();
+  if (!options) {
+    options = { deserializers };
+  } else {
+    options.deserializers = deserializers;
+  }
   const data = core.deserialize(messageData.data, options);
 
   for (let i = 0; i < arrayBufferIdsInTransferables.length; ++i) {

libs/core/01_core.js

@@ -683,6 +683,14 @@
     transferableResources[name] = { send, receive };
   };
   const getTransferableResource = (name) => transferableResources[name];
+  const cloneableDeserializers = { __proto__: null };
+  const registerCloneableResource = (name, deserialize) => {
+    if (cloneableDeserializers[name]) {
+      throw new Error(`${name} is already registered`);
+    }
+    cloneableDeserializers[name] = deserialize;
+  };
+  const getCloneableDeserializers = () => cloneableDeserializers;
 
   // A helper function that will bind our own console implementation
   // with default implementation of Console from V8. This will cause
@@ -1025,11 +1033,13 @@
     hostObjectBrand,
     registerTransferableResource,
     getTransferableResource,
+    registerCloneableResource,
+    getCloneableDeserializers,
     encode: (text) => op_encode(text),
     encodeBinaryString: (buffer) => op_encode_binary_string(buffer),
     decode: (buffer) => op_decode(buffer),
     structuredClone: (value, deserializers) =>
-      op_structured_clone(value, deserializers),
+      op_structured_clone(value, deserializers ?? cloneableDeserializers),
     serialize: (
       value,
       options,

libs/core/ops_builtin_v8.rs

@@ -848,7 +848,7 @@ pub fn op_serialize<'s, 'i>(
   }
 }
 
-#[op2]
+#[op2(reentrant)]
 pub fn op_deserialize<'s, 'i>(
   scope: &mut v8::PinScope<'s, 'i>,
   #[buffer] zero_copy: JsBuffer,