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

examples/postly/build.yaml

@@ -0,0 +1,27 @@
+targets:
+  $default:
+    builders:
+      cherrypick_generator|inject_generator:
+        options:
+          build_extensions:
+            '^lib/app.dart': ['lib/generated/app.inject.cherrypick.g.dart']
+          output_dir: lib/generated
+        generate_for:
+          - lib/**.dart
+      cherrypick_generator|module_generator:
+        options:
+          build_extensions:
+            '^lib/di/{{}}.dart': ['lib/generated/di/{{}}.module.cherrypick.g.dart']
+          output_dir: lib/generated
+        generate_for:
+          - lib/**.dart
+
+#targets:
+#  $default:
+#    builders:
+#      cherrypick_generator|module_generator:
+#        generate_for:
+#          - lib/**.dart
+#      cherrypick_generator|inject_generator:
+#        generate_for:
+#          - lib/**.dart