Stubs are not generated when using the builder api

[ju1ius]

Hi!

When using the builder APIs, classes/functions are properly registered but their stubs are not generated.

Component	Version
ext_php_rs	git:master
cargo-php	v0.1.7

Extension code:

#[php_class(name = "Example\\Foo")]
pub struct Foo;

#[php_startup]
pub fn module_startup() {
  let _ = ClassBuilder::new("Example\\Bar").build().unwrap();
}

#[php_module]
pub fn get_module(module: ModuleBuilder) -> ModuleBuilder {
    module
}

Expected stubs:

<?php

namespace Example {
  class Foo {}
  class Bar {}
}

Actual stubs:

<?php

namespace Example {
  class Foo {}
}