test: 100% coverage for vertical_horizontal_filter + z_score + vpt + csv + adl (#31)

* test(vertical_horizontal_filter): cover period accessor + name metadata

Codecov flagged 6 lines (file at 94.44%): period (61-63) + name (119-121).

* test(z_score): cover period accessor + name metadata

Codecov flagged 6 lines (file at 93.75%): period (59-61) + name (106-108).

* test(vpt): cover value() Some branch, name, zero-prev fallback

Codecov flagged 5 lines (file at 94.38%): value() Some branch (57),
prev==0.0 ROC fallback (77), and Indicator-impl name (100-102).
Add accessors_and_metadata covering value()/name and zero_previous_
close_contributes_zero — feeding a 0.0 baseline + non-zero candle
proves the divide-by-zero guard yields a 0 contribution rather than NaN.

* test(csv): cover from_csv_reader + kill rejects_header dead panic arm

Codecov flagged 5 lines in csv.rs (file at 96.98%): from_csv_reader
(201-204) — never called by existing tests which use from_reader /
open — and the cold  arm in
rejects_header_missing_a_column (279). Add from_csv_reader_accepts_a_
prebuilt_reader (demonstrates the API by building a custom-delimited
csv::Reader and passing it in), and refactor the header-missing test
to use a single matches!() assertion so the panic arm is gone.

* test(adl): cover name metadata

Codecov flagged 3 lines (file at 96.84%): Indicator-impl name body (94-96).

crates/wickra-core/src/indicators/vpt.rs

@@ -129,6 +129,30 @@ mod tests {
         assert_relative_eq!(out[2].unwrap(), 20.0 - 600.0 / 11.0, epsilon = 1e-12);
     }
 
+    /// Cover the `value()` Some branch (line 57) and the Indicator-impl
+    /// `name` body (100-102). `reset_clears_state` hits only the None
+    /// branch; the name was never queried.
+    #[test]
+    fn accessors_and_metadata() {
+        let mut vpt = VolumePriceTrend::new();
+        assert_eq!(vpt.name(), "VPT");
+        assert_eq!(vpt.value(), None);
+        vpt.update(candle(100.0, 50.0, 0));
+        assert_eq!(vpt.value(), Some(0.0));
+    }
+
+    /// Cover the `prev == 0.0` defensive branch (line 77) — the previous
+    /// close is exactly 0, making the percentage ROC undefined. The
+    /// indicator must contribute 0 to the running total rather than NaN.
+    #[test]
+    fn zero_previous_close_contributes_zero() {
+        let mut vpt = VolumePriceTrend::new();
+        vpt.update(candle(0.0, 100.0, 0)); // baseline; prev_close = 0
+        let v = vpt.update(candle(50.0, 200.0, 1)).expect("emits");
+        // ROC fallback is 0, so total stays at 0.
+        assert_eq!(v, 0.0);
+    }
+
     #[test]
     fn emits_from_first_candle_at_zero() {
         let mut vpt = VolumePriceTrend::new();