[MAINT] Remove numba as required dependency

[lorentzenchr]

Is your feature request related to a problem? Please describe.
numba is specified as required dependency in requirements.txt, but it does not seem to be used anywhere. As it is a quite heavy dependency and not available on all platforms, could it be considered to be removed?

Describe the solution you'd like
Remove numba as required dependency.

[jbogaardt]

Hi @lorentzenchr. You're correct that there is no direct dependency on numba, but the package does depend on pydata/sparse which has numba as a hard dependency. Until we move off of sparse, I think we're stuck with numba.

[lorentzenchr]

If I understand correctly, the sparse package is used to provide the "array_backend" for the triangle data (triangle.values array). How about making the sparse backend optional? (if sparse is installed it works, if not an informed error message is thrown.)

[pbower]

Hi there,

This is causing compatibility issues, therefore I'm wondering whether it would be ok to bump up the latest version of numba?

It's causing versioning issues as Chainladder is incompatible with Numpy 2.1

So, if one has the latest numpy in the environment / app, which other dependencies often reference, Chainladder is causing issues.

Thanks,
Pete