Add support for fish paths and arrays

[razvanazamfirei]

This PR introduces a feature enhancement allowing users to distinguish between arrays and path series in the fish shell when using xshe. Previously, xshe treated all array inputs as path series, appending the --path argument by default, which limited the usage of non-path arrays.

The update is backwards compatible. Users can now explicitly pass a regular array by using a nested array structure. For example, specifying [["array_element_1", "array_element_2"]] leads to the input being treated as a standard array and flattened when the environment variable is processed.

The PR updates dependencies and resolves several issues that arose from the update.

Closes #162. Furthermore, this PR closes #83 by implementing the XSHE_CONFIG environment variable.

[superatomic]

Thank you so much for your PR! Your interest in this project means a lot to me.

Your issue raised in #162 is definitely one that should be fixed. From a quick glance, your PR looks very solid. I can also see that you've made quite a few improvements to my code, which I appreciate. Unfortunately, I'm a bit busy at the moment, so I might not have time to provide a complete review and get this merged for about a week. I apologize for the delay.