Fix integer type in user defined functions for Helmholtz energy and ideal gas model

Something changed (I think in pyo3) and currently checking the data type in the `components` methods always panics. See [here](https://github.com/feos-org/feos/blob/main/feos-core/src/python/user_defined.rs#L39) (expects `builtins.int` - use to be just `int`). 