Fourier ARDL Methods: Quantile, Nonlinear, Multi-Threshold Unit Root Tests // Comprehensive implementation of advanced ARDL methodologies for cointegration analysis with structural breaks and asymmetric effects. Includes: (1) Fourier Quantile ARDL (FQARDL) - quantile regression with Fourier approximation for analyzing relationships across the conditional distribution; (2) Fourier Nonlinear ARDL (FNARDL) - asymmetric cointegration with partial sum decomposition following Shin, Yu Greenwood- Nimmo (2014) doi:10.1007/978-1-4899-8008-3_9; (3) Multi- Threshold NARDL (MTNARDL) - multiple regime asymmetry analysis; (4) Fourier Unit Root Tests - ADF and KPSS tests with Fourier terms following Enders Lee (2012) doi:10.1016/j.econlet.2012.05.019 and Becker, Enders Lee (2006) doi:10.1111/j.1467-9892.2006.00490.x. Features automatic lag and frequency selection, PSS bounds testing following Pesaran, Shin Smith (2001) doi:10.1002/jae.616, bootstrap cointegration tests, Wald tests for asymmetry, dynamic multiplier computation, and publication-ready visualizations. Ported from Stata/Python by Dr. Merwan Roudane.