Conditional Standard Error of Measurement in Generalizability Theory // Estimates the per-person conditional standard error of measurement (CSEM) under the persons-by-items single-facet crossed design of Generalizability Theory, following Brennan (1998) doi:10.1177/014662169802200401. Implements three estimators of the relative error variance (full, large_a, uncorrelated) and the closed-form absolute error variance, with both analytical and item-resampling bootstrap sampling variances, quadratic smoothing of CSEMs on observed score, D-study extrapolation, and base-graphics plotting.