feat: Supporting SLURM env vars for launching MAPDL configuration

[germa89]

As the title.

The idea is that on SLURM HPC clusters, PyMAPDL will read the SLURM job through the env vars that the SLURM manager creates, so it can launch MAPDL with the appropriate number of cores.

You can see in the code:

options = [
            # 4,  # Fall back option
            SLURM_CPUS_PER_TASK * SLURM_NTASKS,  # (CPUs)
            SLURM_NPROCS,  # (CPUs)
            # SLURM_NTASKS,  # (tasks) Not necessary the number of CPUs,
            # SLURM_NNODES * SLURM_TASKS_PER_NODE * SLURM_CPUS_PER_TASK,  # (CPUs)
            SLURM_CPUS_ON_NODE * SLURM_NNODES,  # (cpus)
        ]
nproc = max(options)

which is the way I use to decide how many cores should MAPDL instance use.

Same with memory:

        if SLURM_MEM_PER_NODE:
            # RAM argument is in MB, so we need to convert
            if SLURM_MEM_PER_NODE[-1] == "T":  # tera
                ram = int(SLURM_MEM_PER_NODE[:-1]) * 10**6
            elif SLURM_MEM_PER_NODE[-1] == "G":  # giga
                ram = int(SLURM_MEM_PER_NODE[:-1]) * 10**3
            elif SLURM_MEM_PER_NODE[-1] == "G":  # mega
                ram = int(SLURM_MEM_PER_NODE[:-1]) * 10**0
            elif SLURM_MEM_PER_NODE[-1].upper() == "k":  # mega
                ram = int(SLURM_MEM_PER_NODE[:-1]) * 10 ** (-3)
            else:
                ram = int(SLURM_MEM_PER_NODE)

I do not use the MAPDL -machines argument to specify the machines used. I don't think it is needed/compatible.

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[germa89]

This PR should be complemented with https://github.com/ansys-internal/rep-orchestration-interfaces library.

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[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬