Add version management, metrics, and trigger code generation tools

New tools added:
- delete_script_project: Full CRUD support for script projects
- list_versions: List all versions of a script
- create_version: Create immutable version snapshots
- get_version: Get details of a specific version
- get_script_metrics: Get execution analytics (active users, executions, failures)
- generate_trigger_code: Generate Apps Script code for time-based and event triggers

Changes:
- Updated auth/scopes.py with script.metrics scope and drive.file for delete
- Updated core/tool_tiers.yaml with new tools in core and extended tiers
- Updated gappsscript/README.md with new features documentation
- Added 8 new unit tests (18 total)

This brings total Apps Script tools from 11 to 17, covering the complete REST API.

core/tool_tiers.yaml

@@ -151,10 +151,16 @@ appscript:
     - create_script_project
     - update_script_content
     - run_script_function
+    - generate_trigger_code
   extended:
     - create_deployment
     - list_deployments
     - update_deployment
     - delete_deployment
+    - delete_script_project
+    - list_versions
+    - create_version
+    - get_version
     - list_script_processes
+    - get_script_metrics
   complete: []