feat: Add optional arguments to script functions

[makspll]

Adds support for non-required arguments, with default values passed in during a call:

    #[test]
    fn test_optional_argument_not_required() {
        let fn_ = |a: usize, b: Option<usize>| a + b.unwrap_or(0);
        let script_function = fn_.into_dynamic_script_function();

        with_local_world(|| {
            let out = script_function
                .call(vec![ScriptValue::from(1)], FunctionCallContext::default())
                .unwrap();

            assert_eq!(out, ScriptValue::from(1));
        });
    }

Also bumps rhai version to actual release