Upgrade pyo3 to 0.28.1, drop python 3.9, add python 3.14, bump to 0.9.0-2

[PaarthShah]

pyo3 upgrade (0.25.1 → 0.28.1):

• Updated Cargo.toml to use pyo3 0.28.1
• Replaced PyObject with Py<PyAny> in __hash__ attributes (curve25519.rs, ed25519.rs)
• Replaced Python::with_gil() with Python::try_attach() (lib.rs, pk_encryption.rs)
• Added #[pyclass(from_py_object)] to Clone types used as function arguments (Curve25519PublicKey, Curve25519SecretKey)

Python version updates:

• Updated GitHub workflow to test Python 3.14 instead of 3.13
• Updated noxfile.py to support Python 3.10-3.14 (dropped 3.9)

Other changes:

• Bumped version to 0.9.0-2
• Updated thiserror dependency (2.0.3 → 2.0.18)
• Fixed Python 3.14 type hint in session_test.py (replaced PEP 695 type statement with TypeAlias)
• Updated Cargo.lock with all transitive dependency upgrades
• Added maturin-generated comment to release.yml