feat: discover uv-managed global Python installations (#380)

The `pet-uv` locator only discovered uv project/workspace virtual
environments (`.venv` with `pyvenv.cfg`). Python versions installed
globally via `uv python install` were not discovered by the Uv locator.

## Changes

- Scan the uv Python install directory (`UV_PYTHON_INSTALL_DIR`, or
platform defaults: `%APPDATA%\uv\python` on Windows,
`~/.local/share/uv/python` on Unix)
- Enumerate subdirectories matching uv's naming convention
(`cpython-X.Y.Z-os-arch-libc`)
- Skip symlinks (Unix) and junctions (Windows) to avoid duplicating
minor-version aliases
- Identify executables under the uv install directory via `try_from()`
- Parse version from directory names with validation (minimum `X.Y`
format)
- Pass `Environment` to `Uv::from()` for env var access

Fixes #379

Author: karthiknadig

Cargo.lock

@@ -6,6 +6,7 @@ license.workspace = true
 
 [dependencies]
 pet-core = { path = "../pet-core" }
+pet-fs = { path = "../pet-fs" }
 pet-python-utils = { path = "../pet-python-utils" }
 serde = {version = "1.0.226", features = ["derive"]}
 toml = "0.9.7"