chore: adopt Dart 3.9 toolchain — honest floor + tall-style reformat (T-353)

Raise the declared minimums in pubspec.yaml to what our deps already
require: Flutter >=3.35.0 / Dart >=3.9.0 (was 3.19.0 / 3.5.0). alchemist
0.12 needs Flutter 3.32; Dart 3.9 first ships in Flutter 3.35, so 3.35 is
the binding floor. Pin the exact build toolchain in .fvmrc (Flutter
3.44.1).

Moving to the Dart 3.9 language level switches `dart format` to the new
"tall" style and enables two new lints. This commit is the resulting
mechanical churn, isolated from any behaviour change:
  - whole-tree `dart format` reformat (tall style)
  - `dart fix` for unnecessary_underscores + use_null_aware_elements

No runtime behaviour change; `make test` green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/kernel/src/commands/keybindings_test.dart

@@ -80,31 +80,19 @@ void main() {
     tearDown(() => kb.clearState());
 
     test('returns null for KeyUpEvent', () {
-      final up = KeyUpEvent(
-        physicalKey: PhysicalKeyboardKey.keyG,
-        logicalKey: LogicalKeyboardKey.keyG,
-        timeStamp: Duration.zero,
-      );
+      final up = KeyUpEvent(physicalKey: PhysicalKeyboardKey.keyG, logicalKey: LogicalKeyboardKey.keyG, timeStamp: Duration.zero);
       expect(KeybindingResolver.fromKeyEvent(up, kb), isNull);
     });
 
     test('returns null when logicalKey has no keyLabel', () {
       // A synthetic logical key with an unassigned id has an empty label.
       final unlabeled = LogicalKeyboardKey(0x1000fffff);
-      final down = KeyDownEvent(
-        physicalKey: PhysicalKeyboardKey.controlLeft,
-        logicalKey: unlabeled,
-        timeStamp: Duration.zero,
-      );
+      final down = KeyDownEvent(physicalKey: PhysicalKeyboardKey.controlLeft, logicalKey: unlabeled, timeStamp: Duration.zero);
       expect(KeybindingResolver.fromKeyEvent(down, kb), isNull);
     });
 
     test('maps a plain KeyDownEvent to a modifier-free Keybinding', () {
-      final down = KeyDownEvent(
-        physicalKey: PhysicalKeyboardKey.keyG,
-        logicalKey: LogicalKeyboardKey.keyG,
-        timeStamp: Duration.zero,
-      );
+      final down = KeyDownEvent(physicalKey: PhysicalKeyboardKey.keyG, logicalKey: LogicalKeyboardKey.keyG, timeStamp: Duration.zero);
       final b = KeybindingResolver.fromKeyEvent(down, kb);
       expect(b, isNotNull);
       expect(b!.key, 'g');
@@ -118,11 +106,7 @@ void main() {
       _holdModifier(PhysicalKeyboardKey.altLeft, LogicalKeyboardKey.altLeft);
       _holdModifier(PhysicalKeyboardKey.metaLeft, LogicalKeyboardKey.metaLeft);
 
-      final down = KeyDownEvent(
-        physicalKey: PhysicalKeyboardKey.keyG,
-        logicalKey: LogicalKeyboardKey.keyG,
-        timeStamp: Duration.zero,
-      );
+      final down = KeyDownEvent(physicalKey: PhysicalKeyboardKey.keyG, logicalKey: LogicalKeyboardKey.keyG, timeStamp: Duration.zero);
       final b = KeybindingResolver.fromKeyEvent(down, kb)!;
       expect(b.key, 'g');
       expect(b.modifiers.toSet(), {'ctrl', 'shift', 'alt', 'cmd'});
@@ -131,7 +115,5 @@ void main() {
 }
 
 void _holdModifier(PhysicalKeyboardKey physical, LogicalKeyboardKey logical) {
-  HardwareKeyboard.instance.handleKeyEvent(
-    KeyDownEvent(physicalKey: physical, logicalKey: logical, timeStamp: Duration.zero),
-  );
+  HardwareKeyboard.instance.handleKeyEvent(KeyDownEvent(physicalKey: physical, logicalKey: logical, timeStamp: Duration.zero));
 }

test/kernel/src/commands/palette_test.dart

@@ -4,11 +4,11 @@ import 'package:clide/kernel/kernel.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 CommandContribution _cmd(String id, {String? title}) => CommandContribution(
-      id: id,
-      command: id,
-      title: title,
-      run: (_) async => IpcResponse.ok(id: '', data: const {}),
-    );
+  id: id,
+  command: id,
+  title: title,
+  run: (_) async => IpcResponse.ok(id: '', data: const {}),
+);
 
 void main() {
   group('PaletteController', () {
@@ -39,15 +39,9 @@ void main() {
 
     test('filter is case-insensitive against title or command', () {
       palette.setFilter('git');
-      expect(
-        palette.filtered().map((c) => c.command).toSet(),
-        {'git.commit', 'git.push'},
-      );
+      expect(palette.filtered().map((c) => c.command).toSet(), {'git.commit', 'git.push'});
       palette.setFilter('PICK');
-      expect(
-        palette.filtered().map((c) => c.command).toSet(),
-        {'theme.pick'},
-      );
+      expect(palette.filtered().map((c) => c.command).toSet(), {'theme.pick'});
     });
 
     test('invoke closes the palette + runs the command', () async {

test/kernel/src/commands/registry_test.dart

@@ -3,12 +3,8 @@ import 'package:clide/extension/extension.dart';
 import 'package:clide/kernel/kernel.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-CommandContribution _cmd(String name, Future<IpcResponse> Function() run) => CommandContribution(
-      id: name,
-      command: name,
-      title: 'cmd $name',
-      run: (_) => run(),
-    );
+CommandContribution _cmd(String name, Future<IpcResponse> Function() run) =>
+    CommandContribution(id: name, command: name, title: 'cmd $name', run: (_) => run());
 
 void main() {
   group('CommandRegistry', () {
@@ -22,12 +18,7 @@ void main() {
 
     test('execute returns the handler response', () async {
       final r = CommandRegistry();
-      r.register(
-        _cmd(
-          'ping',
-          () async => IpcResponse.ok(id: '', data: const {'pong': true}),
-        ),
-      );
+      r.register(_cmd('ping', () async => IpcResponse.ok(id: '', data: const {'pong': true})));
       final resp = await r.execute('ping');
       expect(resp.ok, true);
       expect(resp.data['pong'], true);