Fix for rii encoding problems under windows + windows pytest (for 3.1…

…3 only) (#228)

* Use chardet in RII scripts

* Add windows pytest

* Fix installation of uv

* Us uv install action

* Add dispersion with encoding errors

* Cleanup diff

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Co-authored-by: MarJMue <49639740+MarJMue@users.noreply.github.com>

Fix for wollam data without dpolE (#214)

* Fix for wollam data without dpolE

* Use union typing to support older py versions

* Fix `as_index()` and `as_dielectric()`

* Add test to check if values stay the same after dispersion conversion

* Remove `as_dielectric()`

* Fix tests

* Set rep and single params

* Remove unecessary import

* Update changelog

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Co-authored-by: MarJMue <49639740+MarJMue@users.noreply.github.com>

Prepare 0.21.0