-spec match([map()], map()) -> {[[map()]], [map()]}.

Skill-based strategy — sorts by skill and pairs adjacent players within a configurable skill window that expands over wait time.

Config keys:

• match_size: players per match (default 2)
• skill_window: initial skill difference allowed (default 200)
• skill_expand_rate: window expansion per 5 seconds of wait (default 50)