Generalize regauge! to AbstractVector

[AFeuerpfeil]

Generalize regauge! to work with AbstractVector instead of Vector.
(PS: In the current implementation of the algorithms, this is not an issue, as regauge! is either only called on single tensors like regauge!(AC, C; alg = alg_orth) or broadcasted like regauge!.(temp_Cs, temp_ACs).)

[lkdvos]

It might be reasonable to just delete this and always broadcast, but since it's already there I'm happy to keep it

[AFeuerpfeil]

Whatever you prefer, I don't have a clear preference.
Is there any situation where one might want to use the special vector version to multi-thread over the unit cell?
Then one could use the already existing OhMyThreads.jl interface.