Virtual class for component-association strategies

Implementations declare their applicability to a sampling design and metadata variable, compute one component association, and expose a stable strategy identifier for provenance. Implementations are discovered through the package strategy registry under the "AssociationStrategy" contract.

Fits a declared binary condition, deterministically scaled observed time, their interaction, and optional nuisance fields to one standardized, deterministically oriented component-score vector. The interaction is the proposal-eligible effect.

Fits a binary between-subject condition, deterministically scaled observed time, their interaction, optional nuisance fields, and correlated subject-specific random intercepts and time slopes. The condition-by-time interaction is the proposal-eligible effect.