Allow dash to be set in bands plots.

[pfebrer]

This commit also makes line dash work for the matplotlib backend

One can now use the"dash" key in bands_style, as in all other line style specifications in the viz module:

sisl.get_sile("file.bands").plot(bands_style={"dash": "dot"})

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 66.25%. Comparing base (2b299e3) to head (1c5596d).

Files	Patch %	Lines
src/sisl/viz/figure/matplotlib.py	0.00%	4 Missing :warning:
src/sisl/viz/processors/bands.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #780 +/- ## =========================================== - Coverage 87.36% 66.25% -21.11% =========================================== Files 396 396 Lines 50706 50609 -97 =========================================== - Hits 44298 33530 -10768 - Misses 6408 17079 +10671 ```

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[zerothi]

@pfebrer this one fails CI, bands.py: L132, KeyError.

[pfebrer]

Can you add "dash": "solid" to the default styles here? https://github.com/zerothi/sisl/blob/58f4758438a66f598e6140826a87571c3e047c12/src/sisl/viz/processors/bands.py#L101

I forgot, that should solve it.

[zerothi]

done!