refactor: move future imports to the top

Imports from `__future__` should be the first imports in a file.
If it's not, it will raise a `SyntaxError`.

Author: deepsource-autofix[bot]

src/omnipkg/libresolver.py

@@ -1,5 +1,5 @@
-import ast
 from __future__ import annotations
+import ast
 
 from omnipkg.common_utils import safe_print