grass.script: Reduce use of env in create_location

[wenzeslaus]

• Reduces use of runtime environment in the create_location function (gisenv call removed).
• Reduces scope of gisrc which simplifies cleanup.
• Adds 4 tests for basic creation of the location (project).

[wenzeslaus]

@echoix Only tangentially related to this PR: You may be interested to know that these tests can't run in parallel and that there are other tests like that. The thing is that the only way to set up the runtime environment with location (project) connection is to change the global process state (environmental variables). However, we are moving the API towards a more robust approach, so the limitation will hopefully disappear. Notably, this is about pytest-based tests. The grass.gunitest tests can be highly parallelized. We can have a deeper discussion on the mailing list or in Discussions if you want.

[echoix]

@wenzeslaus

@echoix Only tangentially related to this PR: You may be interested to know that these tests can't run in parallel and that there are other tests like that. The thing is that the only way to set up the runtime environment with location (project) connection is to change the global process state (environmental variables). However, we are moving the API towards a more robust approach, so the limitation will hopefully disappear. Notably, this is about pytest-based tests. The grass.gunitest tests can be highly parallelized. We can have a deeper discussion on the mailing list or in Discussions if you want.

You might be interested in monkeypatch of pytest:
https://docs.pytest.org/en/latest/how-to/monkeypatch.html
https://docs.pytest.org/en/latest/how-to/monkeypatch.html#monkeypatching-environment-variables
https://dev.to/mhihasan/testing-environment-variable-in-pytest-38ec

Sometimes tests need to invoke functionality which depends on global settings or which invokes code which cannot be easily tested such as network access. The monkeypatch fixture helps you to safely set/delete an attribute, dictionary item or environment variable, or to modify sys.path for importing.
...
All modifications will be undone after the requesting test function or fixture has finished. The raising parameter determines if a KeyError or AttributeError will be raised if the target of the set/deletion operation does not exist.
...
3. Modifying environment variables for a test e.g. to test program behavior if an environment variable is missing, or to set multiple values to a known variable. monkeypatch.setenv and monkeypatch.delenv can be used for these patches.
4. Use monkeypatch.setenv("PATH", value, prepend=os.pathsep) to modify $PATH, and monkeypatch.chdir to change the context of the current working directory during a test.