Removed module-level world variable and replaced all world.wrap() calls
with player.location.wrap(). Added Zone assertion for type safety,
matching the pattern in movement.py. Updated tests to remove fly.world
injection since it's no longer needed.
Each cloud in the trail gets a slightly longer TTL than the one
before it (0.15s stagger). The origin cloud dissolves first, then
each subsequent tile follows. Two consecutive flights produce a
trail where the oldest clouds are already gone.
fly with no args toggles flying on/off. Movement commands (fly east,
etc) only work while airborne. "You aren't flying." if you try to
move without toggling on first. Player.flying field tracks the state.
fly <direction> moves the player 5 tiles, ignoring terrain. Leaves
a trail of bright white ~ clouds that fade after 2 seconds. Effects
system supports arbitrary timed visual overlays on the viewport.
TinTin aliases: fn/fs/fe/fw/fne/fnw/fse/fsw.
