Autots

* transformer bug fixes
* Prophet package adjustments
* linear model singular matrix handling

* bug fix for transformer_list="all"

* minor tweaks and bug fixes
* updated python version required to 3.9 to allow more typing options
* validation_indexes can now be a list of tuples with mixed forecast lengths
* "mixed_length" validation option, for limited testing of longer forecast lengths
* kalman method for ensemble aggregation (ala sensor fusion)
* UpscaleDownscaleTransformer added
* PreprocessingExperts model added (experimental)

* minor adjustments and bug fixes for scalability
* added BallTreeRegressionMotif

* export_template added focus_models option
* added OneClassSVM and GaussianMixture anomaly model options
* added plot_unpredictability_score
* added a few more NeuralForecast search options
* bounds_only to Constraint transformer
* updates for deprecated upstream args
* FIRFilter transformer added
* mle and imle downscaled to reduce score imbalance issues with these two in generate score
* SectionalMotif now more robust to forecast lengths longer than history
* new transformer and metric options for SectionalMotif
* NaN robustness to matse
* 'round' option to Constraint
* minor change to mosaic min style ensembles to remove edge case errors
* 'mosaic-profile', 'filtered', 'unpredictability_adjusted' and 'median' style mosaics added
* updated profiler, and improved feature generation for horizontal generalization
* changepoint style trend as an option to GLM and GLS
* added ShiftFirstValue which is only a minor nuance on PositiveShift transformer
* added BasicLinearModel model
* datepart_method, scale, and fourier encodig to WindowRegression
* trimmed_mean and more date part options to SeasonalityMotif
* some additional options to MultivariateRegression
* added ThetaTransformer
* added TVVAR model (time varying VAR)
* added ChangepointDetrend transformer
* added MeanPercentSplitter transformer
* updated load_daily with more recent history
* added support for passing a custom metric

* Constraint transformer added
* historical_growth constraint method added
* fft as multivariate_feature for Cassandra
* None trend_window now searched as part of Cassandra
* "quarterlydayofweek" method added for datepart
* threshold_method arg to AlignLastValue
* general tempate updated
* slight change to MATSE metric, now only abs values for scaling
* additional args to DatepartRegression
* bug fixes