[jinglemansweep]

This pull request introduces new test fixtures and updates the project configuration to migrate from Poetry to PEP 621 and Setuptools. The main changes enable more robust and maintainable testing for the MeshCore API, including reusable pytest fixtures and sample data for events and tags.

Project configuration migration:

• Migrated pyproject.toml from Poetry to PEP 621 and Setuptools, updating metadata, dependencies, scripts, and build system configuration. This makes the project compatible with standard Python packaging tools and simplifies dependency management.

Testing infrastructure improvements:

• Added comprehensive shared pytest fixtures in tests/conftest.py to support database setup, configuration, FastAPI test clients, mock objects, and sample data for MeshCore API tests. These fixtures enable easier and more consistent test writing.

Sample data for tests:

• Added tests/fixtures/sample_events.json containing representative MeshCore event samples for use in integration and unit tests.
• Added tests/fixtures/sample_tags.json with sample node tags, including various value types and realistic data, to support tag-related tests.
• Added tests/fixtures/invalid_tags.json containing examples of malformed or invalid node tags for negative testing scenarios.