refactor: improve typing and delete mutable default arguments

[framunoz]

With respect the PR #409

Some methods uses mutable parameters, for example

We realized that wih Rodrigo some time ago, I would suggest to do it in a follow-up PR

I mentioned that are many mutable parameters. This is the follow-up PR to fix it.

The changes are:

• Improve typing: The list are more specific and the paths can be a Path instance.
• Drop mutable default arguments: Replace empty list with Nones
• Convert a method in static if the method doesn't use anything.

[framunoz]

I realise that in the module ee_image in the function plot_hist appears the following lines:

eeBands = ee.List(bands) if len(bands) == 0 else self._obj.bandNames()
eeLabels = ee.List(labels).flatten() if len(labels) == 0 else eeBands

That is, if the bands list is empty, it creates a list of bands. If the bands list is not empty, it uses all bands. Is this correct? If so, I think there is a bug in this function.