pub fn php_function_impl(&self) -> TokenStream {
        let internal_ident = self.internal_ident();
        let builder = self.function_builder(CallType::Function);

        quote! {
            #[doc(hidden)]
            #[allow(non_camel_case_types)]
            struct #internal_ident;

            impl ::ext_php_rs::internal::function::PhpFunction for #internal_ident {
                const FUNCTION_ENTRY: fn() -> ::ext_php_rs::builders::FunctionBuilder<'static> = {
                    fn entry() -> ::ext_php_rs::builders::FunctionBuilder<'static>
                    {
                        #builder
                    }
                    entry
                };
            }
        }
    }
Generates a struct and impl for the `PhpFunction` trait.
crates/macros/src/function.rs