Provides S7-based infrastructure for fitting mediation models,
extracting path coefficients, and performing bootstrap inference. Designed
as a foundation package for the mediation analysis ecosystem, supporting
'probmed', 'RMediation', and 'medrobust' packages. Implements unified interfaces
for model fitting across different engines (currently generalized linear models,
with future support for mixed models and Bayesian methods), standardized
extraction of mediation paths from various model types, and robust bootstrap
inference methods. Mediation methods are described in MacKinnon, Lockwood and
Williams (2004)