Avoid enumerating sources in errors for path Python requests (#13335)

e.g., these are misleading cruft in the error message at
https://github.com/astral-sh/uv/pull/12168#discussion_r2078204601

```
❯ uv python find /foo/bar
error: No interpreter found for path `/foo/bar` in virtual environments, managed installations, or search path
❯ cargo run -q -- python find /foo/bar
error: No interpreter found at path `/foo/bar`
```

crates/uv-python/src/discovery.rs

@@ -2646,6 +2646,12 @@ impl fmt::Display for PythonNotFound {
             PythonRequest::Default | PythonRequest::Any => {
                 write!(f, "No interpreter found in {sources}")
             }
+            PythonRequest::File(_) => {
+                write!(f, "No interpreter found at {}", self.request)
+            }
+            PythonRequest::Directory(_) => {
+                write!(f, "No interpreter found in {}", self.request)
+            }
             _ => {
                 write!(f, "No interpreter found for {} in {sources}", self.request)
             }