fix(kit): resolve version aliases to ints in Artifact.from_uri

[andrewwhitecdw]

Problem

Artifact.from_uri("art://name:prod") (alias version) stored the alias string in artifact._version, which is typed int | None. The uri/art_path properties then emit a corrupted URI:

art = Artifact.from_uri("art://a:prod")
art._version   # 'prod'  (str, should be int)
art.uri        # 'art://a:vprod'  -> unresolvable on round-trip

Fix

In from_uri, only assign _version directly when the parsed version is an int; resolve alias strings through the registry entry's alias table, falling back to the latest version.

All URI forms now round-trip correctly:

art://a:prod   -> _version=1  uri=art://a:v1
art://a:v1     -> _version=1  uri=art://a:v1
art://a:1      -> _version=1  uri=art://a:v1
art://a:latest -> _version=1  uri=art://a:v1
art://a        -> _version=1  uri=art://a:v1

Testing

• Reproduced the bug and verified the fix with a local fsspec registry (alias prod -> v1)
• pytest tests/kit — 90 passed