Add kaya_variables, kaya_factors, and kaya_lmdi methods to the comput…

[zacharyschmidt]

…e module. Also add the kaya subdirectory that contains the implementation for the kaya methods. (#875)

Please confirm that this PR has done the following:

• Tests Added
• Documentation Added
• Name of contributors Added to AUTHORS.rst
• Description in RELEASE_NOTES.md Added

Description of PR

This PR adds three methods to the public api of the compute module: kaya_variables(), kaya_factors(), and kaya_lmdi(). The implementation for these methods is in the new kaya submodule.

[codecov]

Codecov Report

Attention: Patch coverage is 96.14325% with 14 lines in your changes missing coverage. Please review.

Project coverage is 95.1%. Comparing base (ddbb88e) to head (b741dbb).
Report is 33 commits behind head on main.

Files with missing lines	Patch %	Lines
pyam/compute.py	87.2%	7 Missing ⚠️
pyam/kaya/kaya_factors.py	88.8%	4 Missing ⚠️
pyam/kaya/kaya_variables.py	94.9%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #884     +/-   ##
=======================================
+ Coverage   95.0%   95.1%   +0.1%     
=======================================
  Files         64      74     +10     
  Lines       6134    6579    +445     
=======================================
+ Hits        5828    6260    +432     
- Misses       306     319     +13     

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[danielhuppmann]

Thanks for the PR! Looks like the legacy-test is failing is because the unit's are ordered differently

model   scenario region variable unit                        year              
model_a scen_a   World  GNP/P    USD * billion / a / million 2010    NaN  0.006
                                 USD * billion / million / a 2010  0.006    NaN

Will take a look more closely next week, don't worry about the failing test for now, will think about how to avoid that.