Add ultranest sampler

[JoranAngevaare]

• Add new sampler method https://johannesbuchner.github.io/UltraNest/using-ultranest.html
• Excellent package for sampling, very easy to install and has a nice pythonic interface.

Probably would have started out with this package instead of pymultinest as the main sampling method if I would have known about it earlier.

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 1.12%.

Quality metrics	Before	After	Change
Complexity	4.23 ⭐	4.03 ⭐	-0.20 👍
Method Length	74.30 🙂	78.67 🙂	4.37 👎
Working memory	10.60 😞	11.12 😞	0.52 👎
Quality	66.23% 🙂	65.11% 🙂	-1.12% 👎

Other metrics	Before	After	Change
Lines	408	466	58

Changed files	Quality Before	Quality After	Quality Change
dddm/context.py	65.76% 🙂	65.76% 🙂	0.00%
dddm/samplers/init.py	%	%	%
dddm/samplers/multi_detectors.py	67.23% 🙂	63.95% 🙂	-3.28% 👎

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

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
dddm/context.py	Context.get_sampler_for_detector	10 🙂	246 ⛔	20 ⛔	33.49% 😞	Try splitting into smaller methods. Extract out complex expressions
dddm/samplers/multi_detectors.py	CombinedMultinest.__init__	1 ⭐	168 😞	19 ⛔	48.50% 😞	Try splitting into smaller methods. Extract out complex expressions
dddm/samplers/multi_detectors.py	CombinedNestle.__init__	1 ⭐	168 😞	19 ⛔	48.50% 😞	Try splitting into smaller methods. Extract out complex expressions
dddm/samplers/multi_detectors.py	CombinedUltraNest.__init__	1 ⭐	168 😞	19 ⛔	48.50% 😞	Try splitting into smaller methods. Extract out complex expressions
dddm/context.py	Context._check_sampler_args	3 ⭐	113 🙂	15 😞	56.40% 🙂	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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Help us improve this quality report!

[coveralls]

Pull Request Test Coverage Report for Build 2752921419

• 46 of 46 (100.0%) changed or added relevant lines in 3 files are covered.
• 20 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-51.6%) to 42.913%

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Files with Coverage Reduction	New Missed Lines	%
dddm/recoil_rates/detector_spectrum.py	20	58.33%

Totals
Change from base Build 2752855767:	-51.6%
Covered Lines:	990
Relevant Lines:	2307

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💛 - Coveralls