Add support for python 3.14 and remove support for Python 3.11

[cadenmyers13]

problem

To bump the Python version, all dependencies in the core pack need to support 3.14.

# core pack dependencies
packaging
PyYAML
diffpy.utils
diffpy.srfit
diffpy.structure

solution

Add python 3.14 support when the core pack can support python 3.14

status for each package

diffpy.utils: diffpy/diffpy.utils#360
diffpy.srfit: diffpy/diffpy.srfit#136
diffpy.structure: diffpy/diffpy.structure#148

[cadenmyers13]

@sbillinge I changed this issue a bit. Because cmi's only dependencies (technically) are only those in core, I think this is a good plan moving forward with python version bumps. Essentially just make sure that everything within core supports the latest Python, then we can bump.

How do you feel about doing a minor bump of cmi (3.1.2)? I would like to get the latest example scripts shipped with cmi before grenoble and it seems that we're not going to get the core or pdf pack up to python 3.14 before then. If you agree, I'll change this issue to 3.1.2 release: #96

[sbillinge]

ok, sounds good. We can do a minor bump