Added the initial development version with HC covariance estimators, normal Wald inference, S3 output, and the PublicSchools dataset.
plot() now supports vcov_hc() objects, producing leverage-versus-adjustment-factor graphics for inspecting the relationship between h_t and g_t.
summary() now prints formal test results, confidence interval checks, and optional emoji markers to improve interpretation of robust inference output.
Added tests() as a formal extractor for coefficient-level Wald test results. The function mirrors the API of confint(): an optional parm argument selects coefficients by name or position, and an optional alpha argument recomputes the reject column without affecting the stored p-values or test statistics.
