perf(postgres): allocation-light bytea hex and date-only cells (#1529, #1521)

lib/core/database/postgres_result_cells.dart

@@ -51,10 +51,14 @@ String postgresResultCellToDisplayString(
   }
 
   if (value is DateTime) {
+    final iso = value.toIso8601String();
     if (_isDateOnly(typeOid, dataTypeName)) {
-      return value.toIso8601String().split('T').first;
+      // The text before `T` (also right for years outside 0..9999, which
+      // carry a sign and six digits), without a split() list (#1529).
+      final t = iso.indexOf('T');
+      return t < 0 ? iso : iso.substring(0, t);
     }
-    return value.toIso8601String();
+    return iso;
   }
 
   if (value is bool) return value ? 'true' : 'false';
@@ -77,11 +81,18 @@ String postgresResultCellToDisplayString(
 
 /// PostgreSQL bytea text `\xdeadbeef`.
 String postgresByteaHexDisplay(Uint8List bytes) {
-  final out = StringBuffer(r'\x');
+  // Two lower-case hex digits per byte, written as code units into one buffer:
+  // no toRadixString / padLeft string per byte (#1529, #1521).
+  const hexDigits = '0123456789abcdef';
+  final out = Uint8List(2 + bytes.length * 2);
+  out[0] = 0x5C; // \
+  out[1] = 0x78; // x
+  var k = 2;
   for (final b in bytes) {
-    out.write(b.toRadixString(16).padLeft(2, '0'));
+    out[k++] = hexDigits.codeUnitAt(b >> 4);
+    out[k++] = hexDigits.codeUnitAt(b & 0x0F);
   }
-  return out.toString();
+  return String.fromCharCodes(out);
 }
 
 String postgresByteaHexDisplayFromCell(Object value) {

test/core/database/postgres_result_cells_scanner_test.dart

@@ -0,0 +1,73 @@
+import 'dart:typed_data';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:postgres/postgres.dart';
+import 'package:querya_desktop/core/database/postgres_result_cells.dart';
+
+void main() {
+  group('postgresByteaHexDisplay (#1529, #1521)', () {
+    test('writes \\x and two lower-case hex digits per byte', () {
+      expect(postgresByteaHexDisplay(Uint8List(0)), r'\x');
+      expect(
+        postgresByteaHexDisplay(Uint8List.fromList([0, 1, 15, 16, 171, 255])),
+        r'\x00010f10abff',
+      );
+    });
+
+    test('every byte value maps to its two digits', () {
+      final all = Uint8List.fromList(List.generate(256, (i) => i));
+      final text = postgresByteaHexDisplay(all);
+      expect(text.length, 2 + 512);
+      for (var i = 0; i < 256; i++) {
+        expect(text.substring(2 + i * 2, 4 + i * 2),
+            i.toRadixString(16).padLeft(2, '0'));
+      }
+    });
+
+    test('cell display goes through the same encoder', () {
+      expect(
+        postgresResultCellToDisplayString(Uint8List.fromList([222, 173])),
+        r'\xdead',
+      );
+    });
+  });
+
+  group('date-only cells (#1529, #1521)', () {
+    test('a date column shows only the date', () {
+      expect(
+        postgresResultCellToDisplayString(
+          DateTime.utc(2026, 1, 5),
+          typeOid: Type.date.oid,
+        ),
+        '2026-01-05',
+      );
+      expect(
+        postgresResultCellToDisplayString(
+          DateTime(2026, 1, 5, 13, 30),
+          dataTypeName: 'date',
+        ),
+        '2026-01-05',
+      );
+    });
+
+    test('years outside 0..9999 keep their sign and digits', () {
+      expect(
+        postgresResultCellToDisplayString(
+          DateTime.utc(12000, 3, 4),
+          typeOid: Type.date.oid,
+        ),
+        '+012000-03-04',
+      );
+    });
+
+    test('timestamps keep the full ISO text', () {
+      expect(
+        postgresResultCellToDisplayString(
+          DateTime.utc(2026, 1, 5, 7, 8, 9),
+          typeOid: Type.timestamp.oid,
+        ),
+        '2026-01-05T07:08:09.000Z',
+      );
+    });
+  });
+}