fix[next]: use current working directory as default cache folder root

[egparedes]

Change the root folder of the gt4py cache directory from the system temp folder to the current working directory, which is more visible and also avoids polluting shared filesystems in hpc clusters.

[tehrengruber]

I was always fine with the existing behavior as every project needs to configure this anyway and it shipped around still existing caching issues. Just a couple of notes / observations I thought are worth mentioning:

• DEBUG=True now means we will easily use out-dated cache entries indefinitely since the cache is not cleared anymore on reboot like in tmp and our cache key does not contain e.g. the GT4Py version.
• The caching behavior is now path dependent, if you run a driver script from a different path you will recompile completely.

[havogt]

* `DEBUG=True` now means we will easily use out-dated cache entries indefinitely since the cache is not cleared anymore on reboot like in `tmp` and our cache key does not contain e.g. the GT4Py version.

I see this as an improvement over the previous behavior. Now it is consistent, before it was depending on the stability of your computer.

[egparedes]

GT4Py cartesian, and I believe also DaCe, have always used the current directory as the root for the cache folder, so gt4py.next using the global temp was actually a compatibility-breaking behavior in some way. cPython has a slightly different behavior (it places the bytecode cache folder where the sources are defined) but also doesn't use the global temp.

We should definitely open an issue about gt4py not using its version (or even the python version) for the caching key.