MSTL

A basic implementation of statsforecast MSTL.

https://github.com/Nixtla/statsforecast

https://nixtlaverse.nixtla.io/statsforecast/docs/models/multipleseasonaltrend.html

See the docstrings - https://earthgecko-skyline.readthedocs.io/en/latest/skyline.custom_algorithms.html#module-custom_algorithms.mstl

See the custom_algorithm source - https://github.com/earthgecko/skyline/blob/master/skyline/custom_algorithms/mstl.py