perf(library): build DateFormat and RegExp once instead of per row

The month-year DateFormat was rebuilt for every loaded row and every
fast-scroller drag label; it is now cached per locale tag. Constant-pattern
RegExp objects built per call (or per word) are now static or top-level.

lib/screens/album_screen.dart

@@ -269,6 +269,7 @@ class _AlbumScreenState extends ConsumerState<AlbumScreen>
   }
 
   static final _qualitySeparators = RegExp(r'[\s_-]+');
+  static final _releaseYearPattern = RegExp(r'(\d{4})');
 
   static (String, bool?) _qualitySignature(Track track) => (
     (track.audioQuality ?? '').trim().toLowerCase().replaceAll(
@@ -360,7 +361,7 @@ class _AlbumScreenState extends ConsumerState<AlbumScreen>
 
   String? _releaseYear(String? date) {
     if (date == null || date.isEmpty) return null;
-    final match = RegExp(r'(\d{4})').firstMatch(date);
+    final match = _releaseYearPattern.firstMatch(date);
     return match?.group(1);
   }
 

lib/screens/queue_tab_sections.dart

@@ -13,6 +13,15 @@ class _LibrarySection {
   int get length => end - start;
 }
 
+final _letterPattern = RegExp(r'[\p{L}]', unicode: true);
+
+final _monthYearFormats = <String, DateFormat>{};
+
+DateFormat _monthYearFormat(BuildContext context) {
+  final locale = Localizations.localeOf(context).toLanguageTag();
+  return _monthYearFormats.putIfAbsent(locale, () => DateFormat.yMMMM(locale));
+}
+
 /// First letter of [text] for an alphabetical index; digits and symbols
 /// share `#`.
 String _sectionInitial(String text) {
@@ -20,7 +29,7 @@ String _sectionInitial(String text) {
   for (final character in trimmed.characters) {
     final upper = character.toUpperCase();
     if (upper != character.toLowerCase()) return upper;
-    if (RegExp(r'[\p{L}]', unicode: true).hasMatch(character)) return upper;
+    if (_letterPattern.hasMatch(character)) return upper;
     return '#';
   }
   return '#';
@@ -79,9 +88,7 @@ extension _QueueTabSections on _QueueTabState {
       return _sectionInitial(item.albumName);
     }
     if (_dateSorts.contains(_sortMode)) {
-      return DateFormat.yMMMM(
-        Localizations.localeOf(context).toLanguageTag(),
-      ).format(item.addedAt);
+      return _monthYearFormat(context).format(item.addedAt);
     }
     return null;
   }
@@ -98,9 +105,7 @@ extension _QueueTabSections on _QueueTabState {
     }
     if (_artistSorts.contains(_sortMode)) return _sectionInitial(artist);
     if (_dateSorts.contains(_sortMode)) {
-      return DateFormat.yMMMM(
-        Localizations.localeOf(context).toLanguageTag(),
-      ).format(added);
+      return _monthYearFormat(context).format(added);
     }
     return null;
   }

lib/screens/track_metadata_screen_display.dart

@@ -3,6 +3,8 @@ part of 'track_metadata_screen.dart';
 
 // Display helpers: quality/bitrate labels, service track-id formatting,
 // snackbars, and path formatting.
+final _spotifyTrackIdPattern = RegExp(r'^[A-Za-z0-9]{22}$');
+
 extension _TrackMetadataDisplay on _TrackMetadataScreenState {
   bool _isBitrateFormatValue(String? value) {
     return const {
@@ -61,7 +63,7 @@ extension _TrackMetadataDisplay on _TrackMetadataScreenState {
   String _displayServiceTrackId(String value) {
     final raw = value.trim();
     if (raw.isEmpty) return raw;
-    final spotifyTrackIdPattern = RegExp(r'^[A-Za-z0-9]{22}$');
+    final spotifyTrackIdPattern = _spotifyTrackIdPattern;
 
     if (raw.startsWith('deezer:')) return raw.substring('deezer:'.length);
     if (raw.startsWith('tidal:')) return raw.substring('tidal:'.length);
@@ -91,7 +93,7 @@ extension _TrackMetadataDisplay on _TrackMetadataScreenState {
   String _serviceForTrackId(String value, {required String fallbackService}) {
     final raw = value.trim();
     if (raw.isEmpty) return fallbackService;
-    final spotifyTrackIdPattern = RegExp(r'^[A-Za-z0-9]{22}$');
+    final spotifyTrackIdPattern = _spotifyTrackIdPattern;
 
     if (raw.startsWith('deezer:')) return MusicServices.deezer;
     if (raw.startsWith('tidal:')) return MusicServices.tidal;

lib/widgets/aligned_lyric_pronunciation.dart

@@ -15,6 +15,9 @@ class LyricPronunciationLayout {
   static const _phraseGap = 4.0;
   static const _pronunciationGap = 2.0;
   static const _rowGap = 6.0;
+  static final _whitespaceRun = RegExp(r'\s+');
+  static final _endsWithWhitespace = RegExp(r'\s$');
+  static final _startsWithWhitespace = RegExp(r'^\s');
 
   double get primaryHeight =>
       _rows.fold(0.0, (height, row) => height + row.primaryHeight) +
@@ -42,7 +45,7 @@ class LyricPronunciationLayout {
         maxWidth <= 0) {
       return null;
     }
-    String normalize(String text) => text.replaceAll(RegExp(r'\s+'), '');
+    String normalize(String text) => text.replaceAll(_whitespaceRun, '');
     if (normalize(original.map((word) => word.text).join()) !=
             normalize(line.text) ||
         normalize(pronunciation.map((word) => word.text).join()) !=
@@ -57,8 +60,8 @@ class LyricPronunciationLayout {
     for (var i = 1; i < pronunciation.length; i++) {
       // Preserve syllables inside a word. Providers may split a romanized
       // word into several timed spans without adding whitespace.
-      if (!RegExp(r'\s$').hasMatch(pronunciation[i - 1].text) &&
-          !RegExp(r'^\s').hasMatch(pronunciation[i].text)) {
+      if (!_endsWithWhitespace.hasMatch(pronunciation[i - 1].text) &&
+          !_startsWithWhitespace.hasMatch(pronunciation[i].text)) {
         continue;
       }
       final start = pronunciation[i].time.inMilliseconds;

lib/widgets/audio_info_sheet.dart

@@ -671,9 +671,11 @@ String _peak(double value) {
   return '${value.toStringAsFixed(6)} · ${_db(dbfs).replaceFirst(' dB', ' dBFS')}';
 }
 
+final _numberPattern = RegExp(r'[-+]?\d+(?:\.\d+)?');
+
 /// Reads tag values such as "-6.52 dB" or "0.988831".
 double? _number(Object? raw) {
   if (raw is num) return raw.toDouble();
-  final match = RegExp(r'[-+]?\d+(?:\.\d+)?').firstMatch(raw?.toString() ?? '');
+  final match = _numberPattern.firstMatch(raw?.toString() ?? '');
   return match == null ? null : double.tryParse(match[0]!);
 }