isochrone parallel tests

[knaaptime]

current tests for isochrones fail because multiple processes try to open the h5 file in write mode. Trying to run those tests in sequence (via the same worker?) using a pytest-xdist mark

[knaaptime]

the remaining failure is windows-only and is some typing error coming from an underying C library somewhere (maybe this)? i dunno

FAILED geosnap/tests/test_isochrones.py::test_isos_from_ids - ValueError: Buffer dtype mismatch, expected 'long' but got 'long long'
FAILED geosnap/tests/test_isochrones.py::test_isos_from_gdf - ValueError: Buffer dtype mismatch, expected 'long' but got 'long long'

long type instead of long long?. That is out of scope here, so i'm going to skip the test on windows unless somebody with a windows box wants to look into it more