feat: batch fill pmtiles files

[cka-y]

Summary:
This PR introduces improvements and refactorings to dataset processing and pipeline task creation, especially around handling PMTiles builder tasks and visualization files.
The changes include:

• refactoring the dataset processing pipeline for clarity and maintainability
• moving the PMTiles builder task creation utility to a shared location
• adding support for rebuilding missing visualization files.

Testing tips:
Test in dev by calling:

curl -X POST "https://tasks-executor-dev-978785769226.northamerica-northeast1.run.app" \
-H "Authorization: bearer $(gcloud auth print-identity-token)" \
-H "Content-Type: application/json" \
-d '{
  "task": "rebuild_missing_visualization_files",
  "payload": {
    "dry_run": true 
  }
}'

Please make sure these boxes are checked before submitting your pull request - thanks!

• Run the unit tests with ./scripts/api-tests.sh to make sure you didn't break anything
• Add or update any needed documentation to the repo
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• Linked all relevant issues
• Include screenshot(s) showing how this pull request works and fixes the issue(s)

[Copilot]

Pull Request Overview

This PR introduces functionality for batch filling PMTiles visualization files. The changes enable the automated rebuilding of missing visualization files (PMTiles) for GTFS datasets by implementing a new task system and moving PMTiles builder functionality to shared helpers.

Key changes:

• Added infrastructure for PMTiles builder task queue and IAM permissions
• Implemented a new task executor function to rebuild missing visualization files with comprehensive testing
• Refactored PMTiles builder functionality from batch processing to shared helpers for reusability

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
infra/functions-python/main.tf	Added task queue infrastructure and IAM permissions for PMTiles builder batch processing
functions-python/tasks_executor/src/tasks/visualization_files/rebuild_missing_visualization_files.py	New task implementation to identify and rebuild missing PMTiles visualization files
functions-python/tasks_executor/tests/tasks/vizualisation_files/test_rebuild_visualization_files.py	Comprehensive test suite for the visualization files rebuild functionality
functions-python/tasks_executor/src/tasks/visualization_files/README.md	Documentation for the new visualization files rebuild task
functions-python/tasks_executor/src/main.py	Added new task handler registration for visualization files rebuilding
functions-python/helpers/utils.py	Moved PMTiles builder task creation function to shared helpers
functions-python/helpers/tests/test_helpers.py	Added tests for the moved PMTiles builder function
functions-python/batch_process_dataset/tests/test_pipeline_tasks.py	Removed PMTiles builder tests (moved to helpers)
functions-python/batch_process_dataset/src/pipeline_tasks.py	Refactored to use shared PMTiles builder function
functions-python/batch_process_dataset/src/main.py	Updated DatasetProcessor methods and improved error handling
functions-python/batch_process_dataset/tests/test_batch_process_dataset_main.py	Updated tests to reflect method name changes

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[jcpitre]

Nice work!

[davidgamez]

LGTM!