Suggestion: Move imports to local scope

[zain-sohail]

Due to how the current interface works, all possible dependencies are imported when importing SedProcessor from sed.

I propose we remove the linter for module level imports and import them in scope when necessary. This will reduce first time importing time from ~30 s to something more managable.

[rettigl]

For me, it takes typically 10s max to load. As anyways all calibrators are loaded with the processor, I don't see that we would gain much.

[zain-sohail]

It's about the same for me, except it's much longer on maxwell somehow.

But the main reason I suggested this is for when I am manually testing changes in code, it takes 10 s everytime, even if I load a different module such as config. This is because SedProcessor is loaded automatically and that loads all the subpackages not necessary for the submodule being tested/used. I've also frequently used the io feature standalone to save or load from tiff/h5 etc. so from a user perspective, I find that also useful.

[rettigl]

Please go ahead and make a PR for this if you want.