use constants better

src/world/tiles/constants.rs

@@ -0,0 +1,7 @@
+/// Default A* weight returned for out-of-bounds or unloaded positions.
+/// Matches normal traversable tile weight so pathfinding degrades gracefully.
+pub const ASTAR_DEFAULT_WEIGHT: u8 = 100;
+/// Rolling history length for z-change frame timing in benchmark reporting.
+pub const Z_CHANGE_HISTORY_LEN: usize = 100;
+/// Bytes per megabyte, for memory reporting.
+pub const BYTES_PER_MB: f32 = 1_048_576.0;