Regression Calibration for Measurement Error Correction // Corrects for measurement error in continuous exposures and covariates using regression calibration methods. Provides corrected coefficients, standard errors, p-values, confidence intervals, and variance-covariance matrices for linear and generalized linear outcome models under an external validation study design. Implements the deattenuation factor method (RegCalibDF) and the substitution approach (RegCalibSub). Supports single and multiple error-prone exposures.