perf(grid): regex-free formatNum and comma-only copies in selection stats (#1531)

lib/features/workspace/grid_selection_calc_engine.dart

@@ -131,9 +131,11 @@ abstract final class GridSelectionCalcEngine {
 
       distinctSet.add(trimmed);
 
-      // Try parsing numeric values (stripping commas if present)
-      final normalized = trimmed.replaceAll(',', '');
-      final parsed = double.tryParse(normalized);
+      // Try parsing numeric values (stripping commas if present). Most cells
+      // have none, so the stripped copy is only made when there is one.
+      final parsed = double.tryParse(
+        trimmed.contains(',') ? trimmed.replaceAll(',', '') : trimmed,
+      );
       if (parsed != null && !parsed.isNaN && !parsed.isInfinite) {
         numericList.add(parsed);
         sum += parsed;
@@ -260,6 +262,13 @@ abstract final class GridSelectionCalcEngine {
     }
     // Limit decimal precision to 4 decimal places
     final formatted = val.toStringAsFixed(4);
-    return formatted.replaceAll(RegExp(r'0+$'), '').replaceAll(RegExp(r'\.$'), '');
+    // Drop the trailing zeros, then one trailing dot (`3.1400` -> `3.14`,
+    // `10.0000` -> `10`): an index walk, no regex (#1531).
+    var end = formatted.length;
+    while (end > 0 && formatted.codeUnitAt(end - 1) == 0x30) {
+      end--;
+    }
+    if (end > 0 && formatted.codeUnitAt(end - 1) == 0x2E) end--;
+    return end == formatted.length ? formatted : formatted.substring(0, end);
   }
 }

test/features/workspace/grid_selection_calc_format_test.dart

@@ -0,0 +1,40 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:querya_desktop/features/workspace/grid_selection_calc_engine.dart';
+
+void main() {
+  group('GridSelectionCalcEngine.formatNum (#1531)', () {
+    test('trims trailing zeros and a dangling dot', () {
+      expect(GridSelectionCalcEngine.formatNum(null), '-');
+      expect(GridSelectionCalcEngine.formatNum(3.0), '3');
+      expect(GridSelectionCalcEngine.formatNum(3.14), '3.14');
+      expect(GridSelectionCalcEngine.formatNum(0.5), '0.5');
+      expect(GridSelectionCalcEngine.formatNum(-2.5), '-2.5');
+      expect(GridSelectionCalcEngine.formatNum(1 / 3), '0.3333');
+      expect(GridSelectionCalcEngine.formatNum(0.1 + 0.2), '0.3');
+      expect(GridSelectionCalcEngine.formatNum(1234.5678), '1234.5678');
+    });
+
+    test('values that round to a whole number keep their integer zeros', () {
+      expect(GridSelectionCalcEngine.formatNum(2.5000001), '2.5');
+      expect(GridSelectionCalcEngine.formatNum(10.00001), '10');
+      expect(GridSelectionCalcEngine.formatNum(100.00004), '100');
+      expect(GridSelectionCalcEngine.formatNum(0.00001), '0');
+    });
+  });
+
+  group('GridSelectionCalcEngine.compute with thousands separators (#1520)', () {
+    test('commas are stripped only for parsing, distinct keeps the text', () {
+      final stats = GridSelectionCalcEngine.compute(
+        ['1,000', ' 2,500.5 ', 'NULL', '', 'abc', '3', '3'],
+      );
+      expect(stats.totalCount, 7);
+      expect(stats.nullCount, 2);
+      expect(stats.distinctCount, 4); // '1,000', '2,500.5', 'abc', '3'
+      expect(stats.numericCount, 4);
+      expect(stats.sum, 3506.5);
+      expect(stats.min, 3);
+      expect(stats.max, 2500.5);
+      expect(stats.median, closeTo(501.5, 1e-9)); // (3 + 1000) / 2
+    });
+  });
+}