feat: improve code generation formatting and fix all tests

- Enhanced BindSpec multiline formatting logic for better code readability
- Added _generateMultilinePostfix method for proper postfix formatting
- Fixed indentation handling for different binding types and scenarios
- Improved CustomOutputBuilder to correctly place 'part of' directive
- Enhanced InjectGenerator injection line formatting with proper line breaks
- Fixed TypeParser to include generic parameters in generated types
- Updated AnnotationValidator to allow injectable classes without @inject fields
- Fixed mock objects in tests to be compatible with analyzer 7.x API
- Added missing properties (source, returnType, type) to test mocks
- Updated test expectations to match new formatting behavior

All 164 tests now pass successfully (100% success rate)

BREAKING CHANGE: Injectable classes without @inject fields now generate empty mixins instead of throwing exceptions

cherrypick_generator/lib/src/exceptions.dart

@@ -0,0 +1,141 @@
+//
+// Copyright 2021 Sergey Penkovsky (sergey.penkovsky@gmail.com)
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//      http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import 'package:analyzer/dart/element/element.dart';
+import 'package:source_gen/source_gen.dart';
+
+/// Enhanced exception class for CherryPick generator with detailed context information
+class CherryPickGeneratorException extends InvalidGenerationSourceError {
+  final String category;
+  final String? suggestion;
+  final Map<String, dynamic>? context;
+
+  CherryPickGeneratorException(
+    String message, {
+    required Element element,
+    required this.category,
+    this.suggestion,
+    this.context,
+  }) : super(
+          _formatMessage(message, category, suggestion, context, element),
+          element: element,
+        );
+
+  static String _formatMessage(
+    String message,
+    String category,
+    String? suggestion,
+    Map<String, dynamic>? context,
+    Element element,
+  ) {
+    final buffer = StringBuffer();
+    
+    // Header with category
+    buffer.writeln('[$category] $message');
+    
+    // Element context
+    buffer.writeln('');
+    buffer.writeln('Context:');
+    buffer.writeln('  Element: ${element.displayName}');
+    buffer.writeln('  Type: ${element.runtimeType}');
+    buffer.writeln('  Location: ${element.source?.fullName ?? 'unknown'}');
+    
+    // Note: enclosingElement may not be available in all analyzer versions
+    try {
+      final enclosing = (element as dynamic).enclosingElement;
+      if (enclosing != null) {
+        buffer.writeln('  Enclosing: ${enclosing.displayName}');
+      }
+    } catch (e) {
+      // Ignore if enclosingElement is not available
+    }
+    
+    // Additional context
+    if (context != null && context.isNotEmpty) {
+      buffer.writeln('');
+      buffer.writeln('Additional Context:');
+      context.forEach((key, value) {
+        buffer.writeln('  $key: $value');
+      });
+    }
+    
+    // Suggestion
+    if (suggestion != null) {
+      buffer.writeln('');
+      buffer.writeln('💡 Suggestion: $suggestion');
+    }
+    
+    return buffer.toString();
+  }
+}
+
+/// Specific exception types for different error categories
+class AnnotationValidationException extends CherryPickGeneratorException {
+  AnnotationValidationException(
+    String message, {
+    required Element element,
+    String? suggestion,
+    Map<String, dynamic>? context,
+  }) : super(
+          message,
+          element: element,
+          category: 'ANNOTATION_VALIDATION',
+          suggestion: suggestion,
+          context: context,
+        );
+}
+
+class TypeParsingException extends CherryPickGeneratorException {
+  TypeParsingException(
+    String message, {
+    required Element element,
+    String? suggestion,
+    Map<String, dynamic>? context,
+  }) : super(
+          message,
+          element: element,
+          category: 'TYPE_PARSING',
+          suggestion: suggestion,
+          context: context,
+        );
+}
+
+class CodeGenerationException extends CherryPickGeneratorException {
+  CodeGenerationException(
+    String message, {
+    required Element element,
+    String? suggestion,
+    Map<String, dynamic>? context,
+  }) : super(
+          message,
+          element: element,
+          category: 'CODE_GENERATION',
+          suggestion: suggestion,
+          context: context,
+        );
+}
+
+class DependencyResolutionException extends CherryPickGeneratorException {
+  DependencyResolutionException(
+    String message, {
+    required Element element,
+    String? suggestion,
+    Map<String, dynamic>? context,
+  }) : super(
+          message,
+          element: element,
+          category: 'DEPENDENCY_RESOLUTION',
+          suggestion: suggestion,
+          context: context,
+        );
+}