Allow for users to set font styles

[dncnwtts]

I noticed in this function:

Cosmoglobe/cosmoglobe/plot/plottools.py

Line 44 in 9d237ef

def set_style(darkmode=False, font="serif"):

that the user's rcParams are overwritten, and I'm wondering if it's possible to set a flag where this isn't done, assuming the user knows what they want to do.