feat(shorebird_cli): add previews directory to cache (#835)

packages/shorebird_cli/lib/src/cache.dart

@@ -60,6 +60,14 @@ class Cache {
     );
   }
 
+  /// Get a named directory from with the cache's preview directory;
+  /// for example, `foo` would return `bin/cache/previews/foo`.
+  Directory getPreviewDirectory(String name) {
+    return Directory(
+      p.join(shorebirdPreviewsDirectory.path, p.withoutExtension(name)),
+    );
+  }
+
   /// The Shorebird cache directory.
   static Directory get shorebirdCacheDirectory {
     return Directory(
@@ -67,6 +75,13 @@ class Cache {
     );
   }
 
+  /// The Shorebird cached previews directory.
+  static Directory get shorebirdPreviewsDirectory {
+    return Directory(
+      p.join(shorebirdCacheDirectory.path, 'previews'),
+    );
+  }
+
   /// The Shorebird cached artifacts directory.
   static Directory get shorebirdArtifactsDirectory {
     return Directory(

packages/shorebird_cli/lib/src/code_push_client_wrapper.dart

@@ -63,7 +63,7 @@ class CodePushClientWrapper {
   Future<List<AppMetadata>> getApps() async {
     final fetchAppsProgress = logger.progress('Fetching apps');
     try {
-      final apps = (await codePushClient.getApps()).toList();
+      final apps = await codePushClient.getApps();
       fetchAppsProgress.complete();
       return apps;
     } catch (error) {

packages/shorebird_cli/test/src/cache_test.dart

@@ -84,6 +84,40 @@ void main() {
       expect(Cache.new, returnsNormally);
     });
 
+    group('getArtifactDirectory', () {
+      test('returns correct directory', () {
+        final directory = cache.getArtifactDirectory('test');
+        expect(
+          directory.path.endsWith(
+            p.join(
+              'bin',
+              'cache',
+              'artifacts',
+              'test',
+            ),
+          ),
+          isTrue,
+        );
+      });
+    });
+
+    group('getPreviewDirectory', () {
+      test('returns correct directory', () {
+        final directory = cache.getPreviewDirectory('test');
+        expect(
+          directory.path.endsWith(
+            p.join(
+              'bin',
+              'cache',
+              'previews',
+              'test',
+            ),
+          ),
+          isTrue,
+        );
+      });
+    });
+
     group('CachedArtifact', () {
       late CachedArtifact artifact;