fix: adjust OpsTest.tmp_path to avoid os.sep

[tonyandrewmeyer]

When generating the tmp_path, ensure that only characters from the model name that are safe for use in paths are used. This particularly covers the case where the model name is in the form user/name, like MAAS.

Fixes #123

[addyess]

@tonyandrewmeyer looks good -- a few lint issues

[tonyandrewmeyer]

Are there docs somewhere on how to run the tests (locally, not relying on CI)? tox -e lint and tox -e unit both pass locally, using Python 3.11, but fail in the CI, so I must not be running them correctly. tox -e integration fails locally, but with a totally different error to in the CI: RuntimeError: Missing dependency: charm.

[addyess]

This still looks good. I think the unit tests could be a bit easier to reason about

[addyess]

So, that test was kinda confusing to me. Can we do this:

Suggested change

	@patch.object(plugin.OpsTest, "default_model_name", "user/model")
	@patch.object(plugin.OpsTest, "_setup_model", AsyncMock())
	@patch.object(plugin.OpsTest, "_cleanup_models", AsyncMock())
	def test_tmp_path_with_nonpath_chars(pytester):
	pytester.makepyfile(
	f"""
	import os
	from pathlib import Path
	os.environ.update(**{ENV})
	async def test_with_tox(ops_test):
	assert ops_test.tmp_path.name == "user_model0"
	"""
	)
	result = pytester.runpytest()
	result.assert_outcomes(passed=1)
	async def test_tmp_path_with_nonpath_chars(tmp_path_factory, setup_request):
	setup_request.module.__name__ = "user/model"
	ops_test = plugin.OpsTest(setup_request, tmp_path_factory)
	assert ops_test.tmp_path.name.startswith("user_model")

[addyess]

Are there docs somewhere on how to run the tests (locally, not relying on CI)? tox -e lint and tox -e unit both pass locally, using Python 3.11, but fail in the CI, so I must not be running them correctly. tox -e integration fails locally, but with a totally different error to in the CI: RuntimeError: Missing dependency: charm.

if you rebase, you'll see the integration tests are likely going to work after merging #128