[Bug]: slurm.conf editor doesn't correctly handle RebootProgram option

[NucciTheBoss]

Bug Description

The parse_line helper function fails to correctly parse the RebootProgram option after a new slurm.conf file has been dumped by the editor. The issue is caused be the fact that the marshaller does not encapsulate the value of RebootProgram in quotations when dumping the new configuration to a file. The option RebootProgram="/usr/sbin/reboot --reboot" becomes RebootProgram=/usr/sbin/reboot --reboot

Then, if you attempt to re-edit the slurm.conf file, parse_line will split the option into two tokens: "RebootProgram=/usr/sbin/reboot" and --reboot. parse_line will then raise a ValueError because there's no = character in --reboot.

slurmutils/slurmutils/models/model.py

Lines 96 to 98 in b124bab

	opts = shlex.split(line) # Use `shlex.split(...)` to preserve quotation strings.
	for opt in opts:
	k, v = opt.split("=", maxsplit=1)

The easiest fix is to just generalize ReasonCallback to QuoteCallback and then set QuoteCallback as the callback to use when parsing the RebootProgram option.

To Reproduce

from slurmutils.models import SlurmConfig

SlurmConfig.from_str("RebootProgram=/usr/sbin/reboot --reboot")
# See `ValueError` be raised.

Environment

Juju Ubuntu 22.04 LXD image, Python 3.10.12

Relevant log output

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/nucci/git/slurm-charms/venv/lib/python3.12/site-packages/slurmutils/models/slurm.py", line 272, in from_str
    data.update(parse_line(SlurmConfigOptionSet, config))
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/nucci/git/slurm-charms/venv/lib/python3.12/site-packages/slurmutils/models/model.py", line 98, in parse_line
    k, v = opt.split("=", maxsplit=1)
    ^^^^
ValueError: not enough values to unpack (expected 2, got 1)

Additional context

Issue discovered as work on charmed-hpc/slurm-charms#35