Upgrade to Python 3.14 and simplify responses

[YoshihitoAso]

This pull request upgrades the project to Python 3.14 and updates several dependencies and configurations to ensure compatibility and improve security.
It also removes the custom ORJSON response logic, simplifies response handling, and updates exception handlers to use the latest FastAPI status codes.

Dependency and Environment Upgrades:

• Updated Python version to 3.14.2 in Dockerfile, tests/Dockerfile_unittest, and pyproject.toml, and set target-version to py314 in Ruff configuration.
• Upgraded key dependencies: FastAPI, Pydantic, Gunicorn, ruff, uvicorn-worker, and switched from httpx to httpx2. Updated development dependencies accordingly.
• Updated uv version to 0.9.16 and added UV_MALWARE_CHECK=1 to installation commands for enhanced security in both Dockerfiles and Makefile.

Configuration and Tooling:

• Updated .pre-commit-config.yaml to use Ruff 0.15.13 and Python 3.14.
• Added [tool.uv] exclude-newer = "7 days" to pyproject.toml for dependency management.

Codebase Simplification and Compatibility:

• Removed custom ORJSON response handling and related code from app/utils/fastapi_utils.py, simplifying JSON response logic.
• Updated FastAPI exception handlers in app/main.py to use status.HTTP_422_UNPROCESSABLE_CONTENT instead of the deprecated UNPROCESSABLE_ENTITY.
• Updated test client setup in tests/conftest.py to use httpx2.ASGITransport for compatibility with httpx2.

[github-actions]

Coverage Report •

File	Stmts	Miss	Branch	BrPart	Cover	Missing
app
main.py	70	16	8	3	77%	75, 87–88, 102, 108, 127–128, 145, 154–155, 164–165, 176–177, 188–189
app/utils
fastapi_utils.py	3	0	0	0	100%
tests
conftest.py	14	3	0	0	78%	30, 34–35
TOTAL	456	97	76	46	78%

Tests	Skipped	Failures	Errors	Time
6	0 💤	0 ❌	0 🔥	3.376s ⏱️