Extended Instrumental Variables Estimation with Diagnostics // Comprehensive instrumental variables and GMM estimation with automatic diagnostics, inspired by the 'Stata' command 'ivreg2' of Baum, Schaffer, and Stillman (2003) doi:10.1177/1536867X0300300101 and Baum, Schaffer, and Stillman (2007) doi:10.1177/1536867X0800700402. Supports 2SLS, LIML, Fuller, k-class, two-step efficient GMM, and continuously- updated (CUE) estimators. Provides classical, robust, cluster- robust, HAC, and Driscoll-Kraay standard errors. Reports weak identification, underidentification, overidentification, and endogeneity tests at estimation time. All outputs are verified against 'Stata' within tight numerical tolerances.