Test config path resolution across Windows drives.

There is a potential issue with the way in which file paths in configurations are resolved across Windows drive letters. We need to add some windows specific tests that check whether resolution is working correctly.

> I didn't checked this back in the day, so I mention it here now. This will work totally find in Mac and Linux (bugs aside) but will fail in Windows if any of the paths is in a different unit than the configuration file. Let's say your config file is in `C:` but you have all you data files in a separate drive, eg. `D:`. In this case, there will be an error as it is not possible to stablish relative paths between locations in different units. It's a very specific case, but I mention it because I learn it the hard way!

_Originally posted by @dalonsoa in https://github.com/ImperialCollegeLondon/virtual_ecosystem/pull/716#discussion_r1939398573_

I think we can do this with:

```python
import platform
@pytest.mark.skipif(platform.system() != "Windows")
```

See also demo of the issue here: https://github.com/ImperialCollegeLondon/virtual_ecosystem/pull/716#discussion_r1940970528

Locate the configuration path-resolution code and existing path tests, then review the linked pull-request discussion and demo. Add Windows-only coverage for configurations and data files on different drive letters, and confirm the test captures the expected resolution behavior.

Written by the indexing model from the issue text.