Augment a worker-fit to the LossFit schema

Worker fits (CLFit, EDFit, SAFit, BFFit, CCFit) each have their own slot layouts. This helper adds missing slots (loss_ata_fit, premium_ata_fit, premium_fit, ed, factor, selected, usage, ci_type, conf_level, bootstrap) as NULL if absent, ensures $full carries the dispatcher-uniform columns (premium_obs, premium_proj, incr_premium_proj, loss_ci_lo, loss_ci_hi, loss_total_cv), and assigns class "LossFit".

For "cl", this synthesizes the premium columns by running an fit_premium() internally when none are present.

Usage

.lossfit_augment(
  fit,
  triangle,
  method,
  premium_fit,
  premium_method,
  premium_alpha,
  sigma_method,
  recent,
  regime,
  maturity_arg,
  conf_level
)