Just changing the types on those two resolved everything, and tests

Just changing the types on those two resolved everything, and tests
pass!

--- a/src/monocypher.c
+++ b/src/monocypher.c
-u64 lane         =
+u32 lane         =
...
-u64  ref       = (window_start + z) % lane_size;
+u32  ref       = (window_start + z) % lane_size;
-u32  index     = (u32)(lane * lane_size) + (u32)ref;
+u32  index     = lane * lane_size + ref;