Fix type signature of Arrow.__getattr__

[salty-horse]

Pull Request Checklist

• 🧪 Added tests for changed code.
• 🛠️ All tests pass when run locally (run tox or make test to find out!).
• 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• 📚 Updated documentation for changed code.
• ⏩ Code is up-to-date with the master branch.

Description of Changes

Arrow's __getattr__ provides access to datetime attributes that aren't handled by Arrow.
It has this signature:

def __getattr__(self, name: str) -> int

It should return Any, as not all attributes from datetime are ints.

For example, in arrow.now().tzname(), tzname is a function.

I noticed that __getattr__ implements two undocumented attributes: week and quarter. The should be split into their own methods, with a docstring.