fix: fetch proxy compatible with node 24 (#333)

In NodeJS v24 undici Response objects are constructed using a mixin
pattern that looks like this:

```javascript
class Test {
  #prop = "foo"

  get prop() {
    return this.#prop
  }

  static getProp(test) {
    return test.#prop
  }
}

function mixin(prototype, getInternal) {
  const methods = {
    status() {
      return getInternal(this)
    },
  }

  Object.assign(prototype.prototype, methods)
}

mixin(Test, Test.getProp)

const test = new Test()
const proxied = new Proxy(test, {
  get(target, prop) {
    const r = Reflect.get(target, prop)

    if (typeof r === "function") {
      return r.bind(target)
    }
    return r
  },
})

console.log(test.prop)
console.log(test.status())
console.log(proxied.prop)
console.log(proxied.status())
```

If we don't bind functions, then we'll get errors like this:
```shell
  return test.#prop
                ^

TypeError: Cannot read private member #prop from an object whose class did not declare it
    at getProp
    at Proxy.status
    at Object.<anonymous>
```

Author: mnahkies

packages/typescript-fetch-runtime/src/common.ts

@@ -38,12 +38,21 @@ export function responseValidationFactoryFactory<Schema>(
     }
 
     return new Proxy(res, {
-      get(target, prop, receiver) {
+      get(target, prop) {
         if (prop === "json") {
           return json
         }
 
-        return Reflect.get(target, prop, receiver)
+        const result = Reflect.get(target, prop)
+
+        // undici does some mixin magic, where it's important that the `this` context
+        // is correct, or else it'll fail to access #private properties on the response
+        // https://github.com/nodejs/undici/blob/edf9b3ff8bfdf5099826b612d8a55572bb707086/lib/web/fetch/response.js#L310
+        if (typeof result === "function") {
+          return result.bind(target)
+        }
+
+        return result
       },
     })
   }