simplified code across the app and consolidated duplicated helpers

lib/widget/prosemirror/pm_image_view.dart

@@ -123,19 +123,14 @@ class PmImageView extends StatelessWidget {
 
   double? _resolveWidth(String? width, double available) {
     if (width == null) return null;
-    final match = RegExp(r'^(\d+(?:\.\d+)?)(px|%|em|rem)$').firstMatch(width);
-    if (match == null) return null;
-    final value = double.parse(match.group(1)!);
-    final double resolved;
-    switch (match.group(2)) {
-      case '%':
-        resolved = available * value / 100;
-      case 'em':
-      case 'rem':
-        resolved = value * 16;
-      default:
-        resolved = value;
-    }
+    final length = parsePmCssLength(width);
+    if (length == null) return null;
+    final value = length.value;
+    final resolved = switch (length.unit) {
+      '%' => available * value / 100,
+      'em' || 'rem' => value * 16,
+      _ => value,
+    };
     return resolved.clamp(1, available);
   }
 }