fix: fetch proxy compatible with node 24

[mnahkies]

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

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:

  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>