Bug fixes to arcgisimage

[nitram96]

fixed bugs with using cachedir in arcgisimage.
cachedir is no longer ignored if verbose is false
if a cached image is found, now correctly shows it using self.imshow()
changed to use os.path.join to join cachedir and filename, so a backslash is no longer required at the end of cachedir

[molinav]

Thanks, @nitram96! It is clear that your changes are correct, let's wait for the workflows to finish and I merge it.

Hopefully I will find some time to increase the coverage of the library. With more tests I would not have overlooked this bug.

[molinav]

@nitram96 Sorry for the delay, everything looks fine, but I would like to add a couple of unit tests before merging. I hope to find some time within the next 2 days, and then most likely I will tag as basemap release 1.4.1 after the merge, because having such method broken in the latest stable is not nice.

[molinav]

@nitram96 I took the opportunity that you opened the PR to fix a bit more the Basemap.arcgisimage method:

• The method code is now compliant with the most basic flake8 and pylint requirements.
• The docstring has been reformated so that it will get rendered correctly by Sphinx with the current furo theme.
• The cache directory should be created on the fly if saving a cache image for the first time and cachedir is a string corresponding to a non-existing directory. This code block was located at the wrong place, so I moved it accordingly.
• I added a couple of tests for Basemap.arcgisimage using the cachedir argument, one with an existing directory and another with a still non-existing directory.

[molinav]

All seems in order, so I am merging. Thanks again, @nitram96!