Use store loop for sampling extent count

Copilot flagged that SeriesData.each still adds callback binding overhead in the visible-window count path. This keeps the existing scale containment semantics but reads parsed values through the underlying DataStore with a precomputed dimension index.

Constraint: direct min/max checks from scale.getExtent did not preserve the filterMode none regression case

Confidence: high

Scope-risk: narrow

Tested: npm run checktype -- --pretty false

Tested: npm run lint -- --quiet src/processor/dataSample.ts

Tested: git diff --check -- src/processor/dataSample.ts

Tested: test/line-sampling-dataZoom-filterMode.html via Chrome, PASS with store-loop count

Not-tested: Full visual regression suite

Author: susiwen8

src/processor/dataSample.ts

@@ -77,11 +77,14 @@ const indexSampler = function (frame: ArrayLike<number>) {
 function countDataInAxisExtent(data: SeriesData, baseAxis: Axis, baseDim: string) {
     let count = 0;
     const scale = baseAxis.scale;
-    data.each(baseDim, function (value: number) {
+    const store = data.getStore();
+    const dimIdx = data.getDimensionIndex(baseDim);
+    for (let i = 0, len = data.count(); i < len; i++) {
+        const value = store.get(dimIdx, i) as number;
         if (scale.contain(value)) {
             count++;
         }
-    });
+    }
     return count;
 }