Support New Python Union Typing Style

Since Python 3.10 is now officially the min supported version, we should generate code using the new union operator https://docs.python.org/3/whatsnew/3.10.html#pep-604-new-type-union-operator

The new syntax is visually cleaner and offers a better IDE experience as well.

```python
def square(number: Union[int, float]) -> Union[int, float]:
return number ** 2
```

new syntax
```python
def square(number: int | float) -> int | float:
return number ** 2
```