Closes#99
- Add module-level `_user_team_cache` dict with 60-second TTL so
`get_user_major_league_team` is called at most once per minute per
user instead of on every keystroke.
- Reduce `search_players(limit=50)` to `limit=25` to match Discord's
25-choice display cap and avoid fetching unused results.
- Add `TestGetCachedUserTeam` class covering cache hit, TTL expiry, and
None caching; add `clear_user_team_cache` autouse fixture to prevent
test interference via module-level state.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>