fix the old_sigma assertion when lr_adapt=True

[Kreyparion]

The current behavior : the assertion fails when lr_adapt=True and sigma is an integer (like sigma=1) which forces to put sigma = 1.0

With assert isinstance(old_sigma, (int, float)) we allow integer values for sigma

[nomuramasahir0]

Hi @Kreyparion ,

Thank you for the PR.
That's correct, and more than that, this assertion is not needed (as old_sigma is surely int or float).
Could you remove the assert instead of new assert?

[Kreyparion]

Yes,
Thank you for pointing it out,
sigma has already been checked in __init__, so getting rid of the assertion shouldn't be a problem

The other three assertions are also always verified, as their types are always checked beforehand with the "current" variables.

But it might be a good idea to keep them for testing purposes.
Should I delete them too ?

[nomuramasahir0]

Yes, as you said, I think the other three assertions can be removed in the same reason.
I'm glad if you delete them.

[nomuramasahir0]

Thanks! Failed checks are not due to this PR, so let me merge it.

[nomuramasahir0]

#175
I'm sorry, I forgot that these assertions are needed for mypy; therefore, I eventually adopted your first suggestion.
Thanks again!