Fizgig 2.1.1 — uv installer + Python 3.13 cold-install fix

Faster installs and a fix for cold installs on Python 3.13.

Installer

• pip → uv for dependency installation and updates — much faster, with a shared cache across venvs. Thanks to @FNGarvin for this contribution (#6), which also hardens the Windows updater (quoted paths, missing-file guards, real error handling so a failed install no longer reports success).
• uv runs with --link-mode=copy, so installs to a different drive than the uv cache no longer print the "Failed to hardlink" warning.

Fixed

• Python 3.13 cold install — safetensors was pinned to 0.4.5, which has no 3.13 wheel and so tried to compile from source (needs a Rust toolchain) on a fresh 3.13 machine. Bumped to 0.5.3, which ships wheels for 3.12 and 3.13; the full dependency set now installs wheel-only on both. (No effect on existing 3.12 installs.)

Upgrading

Run update_fizgig.bat (or git pull then re-run the installer). Existing venvs will pick up uv on the next update automatically.