Add doc comments to IClusteringModel and related types

[martinjms]

Epic: #95

[martinjms]

Opened PR #100 on branch feat/issue-97-add-doc-comments-to-iclusteringmodel-and (base: epic/test-doc-pass). Added /// doc comments to all public types and their fields in crates/arcane-core/src/clustering_model.rs — WorldStateView, ClusterInfo, PlayerInfo, ClusterDecision, DecisionType, DecisionReason, ModelInfo, ValidationResult, and the IClusteringModel trait. Tests added. Format clean. Ready for review.