`list_files` and `list_folders` don't handle substrings between delimiters correctly

**Describe the bug**

When matching substrings, the current functionality of both `list_files` and `list_folders` requires the full substring between delimiters to be separated.

For example, in the string `"fov1_img.tiff"`:
1. `"fov1"` will match this, but not `"fov"`
2. `"tiff"` will match this, but not `"tif"`
3. `".tiff"` will also not match this, since `"."` is a delimiter. This happens because the current scheme filters out any non-alphanum characters from the string to search (`"fov1_img.tiff"` becomes `["fov1", "img", "tiff"]`).

**Expected behavior**

Bryan's implementation was useful for ezSeg, but we will need to support a more loose matching scheme. An additional flag with extra control flow logic would be the easiest solution. So we'd then support:

1. Exact full matching: the full string has to match
2. Exact delimiter-separated matching: only a part of the string has to match, but that part has to be a portion separated out by delimiters
3. Soft matching: the substring can match any part of the string, regardless of delimiter separation