Validate that discovered interpreters meet the Python preference (#7934)

Closes https://github.com/astral-sh/uv/issues/5144

e.g.

```
❯ cargo run -q -- sync --python-preference only-system
Using CPython 3.12.6 interpreter at: /opt/homebrew/opt/python@3.12/bin/python3.12
Removed virtual environment at: .venv
Creating virtual environment at: .venv
Resolved 9 packages in 14ms
Installed 8 packages in 9ms
 + anyio==4.6.0
 + certifi==2024.8.30
 + h11==0.14.0
 + httpcore==1.0.5
 + httpx==0.27.2
 + idna==3.10
 + ruff==0.6.7
 + sniffio==1.3.1

❯ cargo run -q -- sync --python-preference only-managed
Using CPython 3.12.1
Removed virtual environment at: .venv
Creating virtual environment at: .venv
Resolved 9 packages in 14ms
Installed 8 packages in 11ms
 + anyio==4.6.0
 + certifi==2024.8.30
 + h11==0.14.0
 + httpcore==1.0.5
 + httpx==0.27.2
 + idna==3.10
 + ruff==0.6.7
 + sniffio==1.3.1
```

crates/uv-python/src/environment.rs

@@ -158,8 +158,7 @@ impl PythonEnvironment {
         let installation = match find_python_installation(
             request,
             preference,
-            // Ignore managed installations when looking for environments
-            PythonPreference::OnlySystem,
+            PythonPreference::default(),
             cache,
             preview,
         )? {