feat(generator): support output_dir and build_extensions config for generated files

Now the code generator supports specifying a custom output directory and extension/name template for generated DI files via build.yaml ( and ). This allows placing all generated code in custom folders and using flexible naming schemes.

docs: update all user docs and tutorials to explain new output_dir/build_extensions config

- Added detailed usage and YAML examples to cherrypick_generator/README.md
- Synced full_tutorial_en.md and full_tutorial_ru.md (advanced codegen section) with explanation of new configuration and impact on imports
- Updated quick_start_en.md and quick_start_ru.md to mention advanced customization and point to tutorials
- Added troubleshooting and tips for custom output/imports in docs

cherrypick_generator/lib/inject_generator.dart

@@ -19,6 +19,7 @@ import 'package:build/build.dart';
 import 'package:source_gen/source_gen.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:cherrypick_annotations/cherrypick_annotations.dart' as ann;
+import 'cherrypick_custom_builders.dart' as custom;
 
 /// InjectGenerator generates a mixin for a class marked with @injectable()
 /// and injects all fields annotated with @inject(), using CherryPick DI.
@@ -204,4 +205,4 @@ class _ParsedInjectField {
 ///
 /// Фабрика билдера. Используется build_runner.
 Builder injectBuilder(BuilderOptions options) =>
-    PartBuilder([InjectGenerator()], '.inject.cherrypick.g.dart');
+    custom.injectCustomBuilder(options);