Function pathlib_normalize 

pub fn pathlib_normalize(path: &str, fmt: PathFormat) -> String

Canonicalize a filesystem path the same way Python’s pathlib does on construction.

Mirrors pathlib.PurePath’s _format_parsed_parts / _load_parts machinery for filesystem inputs (POSIX and Windows). The transformation is intentionally distinct from normalize (the private trailing-separator stripper above) — pathlib_normalize is what the public path() constructor runs on its argument so that downstream operations see a canonical form, exactly as pathlib does.

Rules (POSIX):

• empty input → "."
• exactly two leading / → preserved (POSIX double-slash root)
• 1 or 3+ leading / → collapsed to a single /
• drop interior . segments (a/./b → a/b)
• drop empty segments from runs of separators (a//b → a/b)
• strip trailing separators (a/b/ → a/b)
• .. segments are kept verbatim (a/../b is NOT simplified; pathlib does not resolve .. because it cannot do so safely without filesystem access)
• dot path . and empty input both render as "."

Rules (Windows):

• same dot/empty rules as POSIX
• all / are converted to \
• drive-relative anchors C: (no separator) are preserved as C:, drive-absolute anchors C:\ keep their trailing \
• UNC anchors \\server\share always end with \
• a single leading \ (rooted-no-drive) is preserved

URIs are NOT handled here — the caller routes URI inputs (uri_path::is_uri) to the URI codepath which preserves every byte verbatim. URIs are opaque per the OpenJD spec (see specifications wiki §1.2.1 path types).