Add option for default python version

[rsyring]

How would this feature be useful?

Remove's the need to specify the python version for every session.

Describe the solution you'd like

Something like:

options.default_pythons = ['3.12']

@session()
def alpha(session: Session):
    pass

@session()
def bravo(session: Session):
    pass

Would act as if you had ran:

@session(python=['3.12'])
def alpha(session: Session):
    pass

@session(python=['3.12'])
def bravo(session: Session):
    pass

Describe alternatives you've considered

I currently set the default as a variable and then use that with each decorator call. But it would be cleaner to set it once and not have as many params in the decorator.

Anything else?

Great library/utility, thanks.