[Feature]: Add support for Python 3.14

[rly]

What would you like to see added to PyNWB?

Python 3.14 was released on Oct 7, 2025. Packages are starting to add support for Python 3.14, and we should do the same.

Is your feature request related to a problem?

No response

What solution would you like?

Add CI testing for Python 3.14 and note support in pyproject.toml and docs.

Do you have any interest in helping implement the feature?

Yes.

Code of Conduct

• [x] I agree to follow this project's Code of Conduct
• [x] Have you checked the Contributing document?
• [x] Have you ensured this change was not already requested?