Is your feature request related to a problem? Please describe.
GdScript defines a setget that can be placed on a property like so:

var my_var setget my_var_set, my_var_get


func my_var_set(new_value):
    my_var = new_value


func my_var_get():
    return my_var # Getter must return a value.

Describe the solution you'd like
An attribute can be added to support this behavior:

#[gdrust(extends = Node)]
struct HelloWorld {
    #[export_range(0.0, 10.0)]
    #[setget(my_getter, my_setter)]
    simple_range: f32,
}

impl HelloWorld {
    fn my_getter(&self, owner: TRef<Node>) -> f32 {
        ...
    }
    
    fn my_setter(&self, owner: TRef<Node>, value: f32) {
        ...
    }
}

If a setget is defined, we should remove the field from the struct.

Describe alternatives you've considered
No alternatives. This seems to be the best without question.