- Redesign TargetInterface and Target base class for better separation of concerns
- Move common validation logic (data/table validation) to base Target class
- Update BigQueryTarget to properly extend base class using super().load()
- Standardize method signatures across target implementations
- Remove client abstraction from base class, keep target-specific
- Improve parameter naming consistency (target_table vs table)

Add Terraform configuration for GCP sandbox environment including:
- BigQuery dataset
- IAM roles and service accounts
- Secret management configuration
- Main infrastructure definitions
- Variable definitions for environment configuration

- Add secret handler module for GCP Secret Manager integration
- Refactor config to support secret references instead of plain passwords
- Update source creation to resolve secrets before database connection
- Add google-cloud-secret-manager dependency
- Remove default values from docker-compose environment variables
- Add project_number field to BigQuery target configuration
- Improve error logging with stack traces in main processing loop

…ucture

- Add comprehensive test suite with 12 new test files covering core, components, integration, and error handling
- Implement Google Cloud Secret Manager integration for secure credential handling
- Add Terraform infrastructure for GCP sandbox environment (BigQuery, IAM, secrets)
- Enhance BigQuery target with improved error handling and configuration
- Refactor core components (catalog, config, extractors, sources) for better modularity
- Add new dependencies: pytest-mock, opentelemetry, google-cloud-secret-manager, pytest-cov
- Remove obsolete devcontainer configuration and hello world test
- Update Docker and Makefile configurations for improved development workflow

Add comprehensive docstring coverage across all modules, classes, and methods.
Fix formatting issues including periods, blank lines, and imperative mood.
Ensure compliance with pydocstyle rules.

Fix formatting and type conflicts