Support Python 3.14 and bump to v0.3.0

[slint]

AI disclaimer: This was mostly done using Claude Code (Opus 4.5 or 4.6 probably), but I had a review of the code and also confirmed that everything works in combination with invenio-swh.

• Format code with ruff
• Replace deprecated imp module with importlib.util
• Fix create_logging_config to write text not binary
• Replace deprecated logging warn() with warning()
• Update Python version classifiers to 3.9-3.14
• Update tox.ini: Python 3.9-3.14, replace nose with pytest
• Rename tests/http to tests/http_tests to avoid shadowing stdlib
• Bump version to 0.3.0