Compute the Bayesian posterior mean given a normal prior and experimental result
Source:R/simulate_posteriors.R
posterior_mean_fn.RdApplies the precision-weighted updating formula from FEDAI Equations 11.2–11.4.
The posterior mean is a weighted average of the prior mean g and the
bias-corrected experimental estimate x_e, where the weights depend on prior
variance, sampling-bias variance, and sampling variance.