refactor: implement Uvicorn factory pattern and clean up test suite

[jonhealy1]

Related Issue(s):

Description:

• Refactored application initialization to completely eliminate global state and natively support the Uvicorn --factory pattern. Replaced the global app variable with a create_app() factory wrapper in app.py, ensuring pristine memory isolation per worker and preventing unintended import side-effects. Additionally, updated the test suite to use the new factory pattern (eliminating shadow implementations) and fixed httpx async client compatibility.

PR Checklist:

• pre-commit hooks pass locally
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.

[vincentsarago]

thanks @jonhealy1

can you also change the Dockerfile

stac-fastapi-pgstac/Dockerfile

Line 33 in 813a002

CMD ["uvicorn", "stac_fastapi.pgstac.app:app", "--host", "0.0.0.0", "--port", "8080"]

oops too fast 😅