vLLM integration: bring Python 3.14 support when implemented in the original library

[anakin87]

Currently, vLLM does not support Python 3.14: vllm-project/vllm#34096

We should monitor the above issue and, when vLLM becomes compatible with 3.14:

• update our pin in pyproject
• test with 3.14 (instead of 3.13)
• add 3.14 information to classifiers in pyproject.toml