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/adl.rs

@@ -127,6 +127,14 @@ mod tests {
         assert!(adl.update(candle(8.0, 10.0, 8.0, 9.0, 50.0, 0)).is_some());
     }
 
+    /// Cover the Indicator-impl `name` body (94-96). The other accessors
+    /// are exercised by existing tests; `name` was never queried.
+    #[test]
+    fn accessors_and_metadata() {
+        let adl = Adl::new();
+        assert_eq!(adl.name(), "ADL");
+    }
+
     #[test]
     fn close_at_high_accumulates_full_volume() {
         // Every bar closes at its high: MFM = +1, so ADL grows by `volume`.