test(resample): cover RolledBar::absorb low-update branch

Codecov flagged a single uncovered line in crates/wickra-data/src/resample.rs:
line 46, the `self.low = c.low;` assignment inside RolledBar::absorb.
None of the existing resampler tests fed a follow-up candle with a strictly
lower low than the first candle in the bucket, so the `c.low < self.low`
branch never fired. Coverage stayed at 122/123.

Add a small dedicated test that pushes a 10.0-low candle into bucket 0, then
a 8.0-low candle into the same bucket, and asserts the rolled bar's low
reflects the dip. Resample file is now at 123/123 lines, no behavioural change.

crates/wickra-data/src/resample.rs

@@ -192,6 +192,20 @@ mod tests {
         assert_eq!(bar.low, 9.0);
     }
 
+    #[test]
+    fn absorb_lowers_low_on_dipping_candle() {
+        // The first candle in the bucket sets low = 10.0; the second dips to
+        // 8.0 and must overwrite. Exercises the `c.low < self.low` branch in
+        // RolledBar::absorb that the other resampler tests never trigger
+        // because their follow-up candles always have a higher low.
+        let mut r = Resampler::new(Timeframe::new(5).unwrap());
+        r.push(c(0, 10.0, 11.0, 10.0, 10.5, 1.0)).unwrap();
+        r.push(c(1, 10.5, 11.5, 8.0, 9.0, 1.0)).unwrap();
+        let bar = r.flush().unwrap().unwrap();
+        assert_eq!(bar.low, 8.0);
+        assert_eq!(bar.high, 11.5);
+    }
+
     #[test]
     fn flushes_a_non_finite_volume_as_an_error() {
         let mut r = Resampler::new(Timeframe::new(5).unwrap());