try to use latest Python

[alaniwi]

For the last release, the "don't downgrade" approach meant that we specified python>=3.10.5 and then mamba chose 3.10.8. A concern has been raised about the support lifetime of 3.10, so next time, let's use >=3.12

if possible - also try a vanilla env + python (e.g. mamba create -n testenv python) and compare the python version that we get in that simple environment with what mamba wants to choose for the full Jaspy environment, just to check that the dependencies aren't causing a significant downgrade. In the worst case, work out which other packages may be responsible and try to decide whether it is a priority to keep them as compared to having a recent Python.

[alaniwi]

For the March 2024 release, the full Jaspy environment will not resolve with 3.12 even though this is available and works for smaller environments. Earlier experimentation suggests that there are more than one package that don't have sufficiently up-to-date conda packages to allow for use of 3.12; it was proving essentially impossible to resolve the enviroment without commenting out a lot of packages. So we are using 3.11.8 this time: an advance on 3.10 but not the latest.