Methods that apply to the parent `nmar_result` class and are not specific to a particular engine (e.g., EL). Engines return a child class (e.g., `nmar_result_el`) that inherits from `nmar_result` and may override or extend behavior.
S3 surface for base `nmar_result`
Result objects expose a universal schema: - `y_hat`, `estimate_name`, `se`, `converged`. - `model`: list with `coefficients`, `vcov`, plus optional extras. - `weights_info`: list with respondent weights and trimming metadata. - `sample`: list with total units, respondent count, survey flag, and `design`. - `inference`: variance metadata (`variance_method`, `df`, diagnostic flags). - `diagnostics`, `meta`, and `extra` for estimator-specific details.
New engines should populate these components in their constructors and rely on the `nmar_result_get_*` utilities when implementing child-specific S3 methods.