`_encode_uri_path_for_uss` does not skip encoded URIs

[traeok]

Describe the bug

_encode_uri_path_for_uss function does not acknowledge encoding on a URI given as input, which can result in invalid URI encoding sequences.

Expected and actual results

Expected: _encode_uri_path_for_uss should either skip encoded URIs, or at least have a note on the function clarifying that it should not be used with a URI that's already encoded.
Actual: The function encodes the URI again, causing incorrect URI encoding.

Example Python logic to detect and return early for this case:

from urllib.parse import unquote

def is_uri_encoded(uri: str) -> bool:
    """Returns True if the URI contains percent-encoded characters."""
    return uri != unquote(uri)

# Examples
print(is_uri_encoded("https://example.com%20world"))  # True
print(is_uri_encoded("https://example.com world"))  # False