docs: Rename caveace asset to cave_ace in our examples (#2304)

I am on a crusade to improve our spellchecking. I have a big PR that I am now going to break down into very small chunks to for review.

Here I am renaming an asset to include a word separator, as the combined word "caveace" doesn't exist. This not only allows us to remove one unclear entry in our dictionary, but make our example code easier to read for new users.

Note: in order to easily update the internal name of the atlas (unrelated to file name), that is stored in the binary, I used this pending feature from Fire Atlas.

.github/.cspell/flame_dictionary.txt

@@ -18,7 +18,6 @@ Tiled
 Tiled's
 Tilemap
 Wyrmsun
-caveace
 erayzesen
 padracing
 ptero

packages/flame/test/cache/assets_cache_test.dart

@@ -34,12 +34,12 @@ void main() {
 
     test('readBinaryFile', () async {
       final assetsCache = AssetsCache(prefix: '');
-      final fileName = fixture('caveace.fa').path;
+      final fileName = fixture('cave_ace.fa').path;
       final file = await assetsCache.readBinaryFile(fileName);
       expect(file, isA<Uint8List>());
 
       expect(
-        () async => assetsCache.readFile(fixture('caveace.fa').path),
+        () async => assetsCache.readFile(fixture('cave_ace.fa').path),
         failsAssert('"$fileName" was previously loaded as a binary file'),
       );
     });

packages/flame_fire_atlas/example/lib/main.dart

@@ -16,7 +16,7 @@ class ExampleGame extends FlameGame with TapDetector {
 
   @override
   Future<void> onLoad() async {
-    _atlas = await loadFireAtlas('caveace.fa');
+    _atlas = await loadFireAtlas('cave_ace.fa');
     add(
       SpriteAnimationComponent(
         size: Vector2(150, 100),

packages/flame_fire_atlas/example/pubspec.yaml

@@ -22,4 +22,4 @@ dev_dependencies:
 flutter:
   uses-material-design: true
   assets:
-    - assets/caveace.fa
+    - assets/cave_ace.fa

packages/flame_fire_atlas/test/flame_fire_atlas_test.dart

@@ -26,7 +26,7 @@ class MockedGame extends Mock implements FlameGame {
 }
 
 Future<Uint8List> readExampleFile() async {
-  final exampleAtlas = File('./example/assets/caveace.fa');
+  final exampleAtlas = File('./example/assets/cave_ace.fa');
   final bytes = await exampleAtlas.readAsBytes();
   return bytes;
 }
@@ -58,7 +58,7 @@ void main() {
   group('FireAtlas', () {
     test('can load the asset', () async {
       final atlas = await readTestAtlas();
-      expect(atlas.id, 'caveace');
+      expect(atlas.id, 'cave_ace');
     });
 
     test('can load the asset using the global assets/images', () async {
@@ -139,7 +139,7 @@ void main() {
     test('converts to json', () async {
       final atlas = await readTestAtlas();
       final json = atlas.toJson();
-      expect(json['id'], 'caveace');
+      expect(json['id'], 'cave_ace');
     });
 
     test('serialize/deserialize', () async {