Add DarkElf + test notebooks

[JoranAngevaare]

Add https://github.com/JoranAngevaare/DarkELF as a dependency

[coveralls]

Pull Request Test Coverage Report for Build 2401458701

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 94.343%

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Files with Coverage Reduction	New Missed Lines	%
dddm/statistics.py	1	90.82%

Totals
Change from base Build 2373046923:	0.04%
Covered Lines:	2118
Relevant Lines:	2245

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💛 - Coveralls

[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 4.31%.

Quality metrics	Before	After	Change
Complexity	0.57 ⭐	0.52 ⭐	-0.05 👍
Method Length	51.22 ⭐	39.57 ⭐	-11.65 👍
Working memory	10.39 😞	9.33 🙂	-1.06 👍
Quality	71.74% 🙂	76.05% ⭐	4.31% 👍

Other metrics	Before	After	Change
Lines	105	63	-42

Changed files	Quality Before	Quality After	Quality Change
tests/test_spectra.py	75.82% ⭐	76.05% ⭐	0.23% 👍

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
tests/test_spectra.py	test_simple_spectrum	0 ⭐	138 😞	13 😞	59.04% 🙂	Try splitting into smaller methods. Extract out complex expressions
tests/test_spectra.py	_galactic_spectrum_inner	2 ⭐	49 ⭐	14 😞	68.04% 🙂	Extract out complex expressions

Legend and Explanation

The emojis denote the absolute quality of the code:

• ⭐ excellent
• 🙂 good
• 😞 poor
• ⛔ very poor

The 👍 and 👎 indicate whether the quality has improved or gotten worse with this pull request.

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Please see our documentation here for details on how these metrics are calculated.

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