fix: resolve remaining clippy errors in ddsketch

- Replace approximate PI/E constants with non-famous value in test
- Fix reversed empty range (2048..0) → (0..2048).rev() in store test

Co-authored-by: Cursor <cursoragent@cursor.com>

sketches-ddsketch/src/encoding.rs

@@ -510,9 +510,7 @@ mod tests {
 
     #[test]
     fn test_var_double_roundtrip() {
-        for v in [
-            0.0, 1.0, 2.0, 5.0, 15.0, 42.0, 100.0, 1e-9, 1e15, 0.5, 3.14159,
-        ] {
+        for v in [0.0, 1.0, 2.0, 5.0, 15.0, 42.0, 100.0, 1e-9, 1e15, 0.5, 7.77] {
             let mut buf = Vec::new();
             encode_var_double(&mut buf, v);
             let mut input = buf.as_slice();

sketches-ddsketch/src/store.rs

@@ -245,7 +245,7 @@ mod tests {
     fn test_simple_store_rev() {
         let mut s = Store::new(2048);
 
-        for i in 2048..0 {
+        for i in (0..2048).rev() {
             s.add(i);
         }
     }