Disable multithreading by default on HPC nodes

[david-zwicker]

Multithreading is enabled by default since it is useful to have during quick exploration, so operators are evaluated more quickly. However, in an HPC environment, the default should probably be a single-threaded application. We could achieve this by providing a new value "only_local" or something like this for the option numba.multithreading. This option would disable multithreading if it detects the environment variable SLURM_JOB_ID, PBS_JOBID, or JOB_ID. Otherwise, multithreading would be enabled.