🩹 Fix deprecation warning for using xr.Dataset.dim

[s-weigand]

This change fixes the deprecation warning:

FutureWarning: The return type of `Dataset.dims` will be changed to return a set of dimension names in future, in order to be more consistent with `DataArray.dims`. To access a mapping from dimension names to lengths, please use `Dataset.sizes`.
  center_λ = min(res.dims["spectral"], round(res.dims["spectral"] / 2))

When center_λ has its default value of None.

However, when fixing this I found that we have a bug.
First of all:

min(res.sizes["spectral"], round(res.sizes["spectral"] / 2))

will always return round(res.sizes["spectral"] / 2) since res.sizes["spectral"] is the length of the spectral coordinate (same goes for the current and past behavior of res.dims["spectral"])

But since this value is later used with xr.DataArray.sel it leads to a wrong behavior since now center_λ isn't a spectral value but the index of it, resulting in the first wavelength being selected.

Example plot for the 4TT case study

Current behavior with omitted center_λ

Current behavior with set center_λ

So I think we should change the fallback to:

center_λ = res.coords["spectral"].mean().item()

or

center_λ = res.coords["spectral"].isel(spectral=res.sizes["spectral"]//2).item()

to take none equidistant spectral axes into account.

Change summary

• 🩹 Fix deprecation warning for using xr.Dataset.dim

Checklist

• ✔️ Passing the tests (mandatory for all PR's)

[github-actions]

👈 Launch a binder notebook on branch s-weigand/pyglotaran-extras/fix-deprecations

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[jsnel]

Historically we've always selected the first wavelength if not explicitly provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 44.77%. Comparing base (b880df9) to head (751a859).
Report is 20 commits behind head on main.

Files with missing lines	Patch %	Lines
pyglotaran_extras/plotting/plot_overview.py	0.00%	1 Missing ⚠️
pyglotaran_extras/plotting/utils.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #267   +/-   ##
=======================================
  Coverage   44.77%   44.77%           
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  Files          27       27           
  Lines        1043     1043           
  Branches      162      162           
=======================================
  Hits          467      467           
  Misses        568      568           
  Partials        8        8           

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[jsnel]

We need to get rid of those spammy deprecations warnings.

Later we'll figure out other improvements.