Current item path should be normalized before comparing against excluded/included paths regex

[noexec]

The plugin uses re.search() with excluded/included paths configuration extracted from pyproject.toml settings.
However, Black docs specify that:

1. Forward slashes are used on all platforms, including Windows (ref)
2. ^/ should match the beginning of path (ref)

This implies that before deciding on inclusion and exclusion, collected file paths should be normalized to / directory separators, and should begin with / as well. E.g., /src/package/file.py.

At present, an excluded path like /src/package/file.py or /file.py fails to exclude it on Windows platform.