Update supported Python versions

[niksirbi]

Python 3.8 is at end of life, i.e. no longer supported.
Should we also drop it? Is anyone using NeuralPlayground in Python 3.8 environments?

At the same time we could add explicit support for Python 3.12 and 3.13.

[adamltyson]

Considering NPG relies on scipy et al., we should probably follow SPEC0.

[niksirbi]

NeuralPlayground now supports 3.11 - 3.13, which is quite up-to-date.

Perhaps we should consider testing on Python 3.14 and dropping 3.11 soon, if we want full SPEC0 compliance.