Shared Generics for the 'r-causal' Ecosystem // A home for the S3 generics shared across the 'r-causal' ecosystem, including 'propensity', 'halfmoon', 'positively', and 'balancing'. Owning the generic definitions in one place lets those packages register methods without masking one another when several are attached at once. The generics cover inverse probability weighted estimation, effective sample size, and the metadata carried by causal weight vectors, and the package supplies the abstract causal weight class and the result class those estimates are returned in, together with the methods both classes carry, so that the ecosystem packages inherit them rather than writing their own. The design follows that of the 'generics' package, which provides commonly used S3 generics for the same purpose: letting packages share a single definition instead of each defining its own.