Run generic simulation-based calibration

Usage

run_sbc(
  simulator,
  fitter,
  posterior_draws,
  replications = 100L,
  seed = 20260808L
)

simulator: Function `simulator(replicate)` returning `list(data, truth)`; `truth` must be a named numeric vector.
fitter: Function `fitter(data)` returning a fitted object.
posterior_draws: Function returning a draws matrix/data frame whose columns match names in `truth`.
replications: Number of SBC replications.
seed: RNG seed.