Add rpds-py dependency to fix ModuleNotFoundError

Co-authored-by: ncrmro <8276365+ncrmro@users.noreply.github.com>

Author: Copilot

flake.nix

@@ -31,6 +31,7 @@
             click
             rich
             jsonschema
+            rpds-py  # Required by jsonschema's referencing dependency
           ];
 
           # Skip tests during build (they can be run in devShell)