Callable not throwing any errors

On gdext 0.2.4 this code properly throws errors:

```rust
let instance: Gd = whatever;

// error because function is not defined
instance.call("_not_real", &[]);
// error because function def has a parameter
instance.call("_param_required", &[]);
```

But when using the Callable, all failures are silent:

```rust
let instance: Gd = whatever;

// nothing happens
instance.callable("_not_real").call(&[]);
// nothing happens
instance.callable("_param_required", &[]);
```

I would expect `callable.call()` here to throw the same errors that `instance.call` and gdscript's `Callable().call()` do. It would also be awesome to have a result on callable, though this deviates from gdscript's behavior:

```rust
let Some(callable) = instance.callable("_not_real") else {
println!("method not found!");
return;
};
```

Start by comparing the behavior shown for instance.call("_not_real") and instance.callable("_not_real").call(&[]) in the Rust bindings. Check how missing methods and missing parameters are handled in each path; done means Callable.call reports the same failures as instance.call, with the optional result behavior clarified by the existing API.

Written by the indexing model from the issue text.