fix(arena): remove unused Gaussian import in test module

src/arena.rs

@@ -25,7 +25,7 @@ impl ScratchArena {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{N_INF, gaussian::Gaussian};
+    use crate::N_INF;
 
     #[test]
     fn reset_keeps_capacity() {