Confirm that the directory name is a valid Python install key during managed check (#16080)

Closes #16077

```
❯ UV_PYTHON_INSTALL_DIR=/opt uv python list --no-managed-python
cpython-3.9.6-macos-aarch64-none    /usr/bin/python3
❯ alias uv=$(pwd)/target/debug/uv
❯ UV_PYTHON_INSTALL_DIR=/opt uv python list --no-managed-python
cpython-3.13.3-macos-aarch64-none     /opt/homebrew/bin/python3.13 -> ../Cellar/python@3.13/3.13.3/bin/python3.13
cpython-3.13.3-macos-aarch64-none     /opt/homebrew/bin/python3 -> ../Cellar/python@3.13/3.13.3/bin/python3
cpython-3.12.10-macos-aarch64-none    /opt/homebrew/bin/python3.12 -> ../Cellar/python@3.12/3.12.10/bin/python3.12
cpython-3.11.12-macos-aarch64-none    /opt/homebrew/bin/python3.11 -> ../Cellar/python@3.11/3.11.12/bin/python3.11
cpython-3.9.6-macos-aarch64-none      /usr/bin/python3
pypy-3.10.14-macos-aarch64-none       /opt/homebrew/bin/pypy3 -> ../Cellar/pypy3.10/7.3.17_1/bin/pypy3
```

Prevents false positives when the `UV_PYTHON_INSTALL_DIR` is a prefix of
some other path with Python installations

Author: zanieb

crates/uv-python/src/interpreter.rs

@@ -3,6 +3,7 @@ use std::env::consts::ARCH;
 use std::fmt::{Display, Formatter};
 use std::path::{Path, PathBuf};
 use std::process::{Command, ExitStatus};
+use std::str::FromStr;
 use std::sync::OnceLock;
 use std::{env, io};
 
@@ -301,7 +302,19 @@ impl Interpreter {
             return false;
         };
 
-        self.sys_base_prefix.starts_with(installations.root())
+        let Ok(suffix) = self.sys_base_prefix.strip_prefix(installations.root()) else {
+            return false;
+        };
+
+        let Some(first_component) = suffix.components().next() else {
+            return false;
+        };
+
+        let Some(name) = first_component.as_os_str().to_str() else {
+            return false;
+        };
+
+        PythonInstallationKey::from_str(name).is_ok()
     }
 
     /// Returns `Some` if the environment is externally managed, optionally including an error