Tstoolbox

Fix

- removed skipna and append="columns" that actually weren't doing anything

Refactor

- refactor with refurb and pylint

Fix

- **fill.py**: force type to be float so that linear (and other mathematical methods) work in fill

Fix

- fixed type hint for plot
- another try to get plot tests to pass on github
- plot tests are failing on github that I can't reproduce locally
- **plot**: reinstated plot tests which are almost identical to plottoolbox tests but use tstoolbox.plot which uses plottoolbox in the background
- moved to the breaking change move in toolbox_utils from typic to pydantic and misc. modernizations