The file catch_conflicts.py is in a subdirectory because, if it isn't, the /nix/store/ directory is added to sys.path, causing a delay when building.
catch_conflicts.py
/nix/store/
sys.path
Pointers:
https://docs.python.org/3/library/sys.html#sys.path
https://github.com/NixOS/nixpkgs/pull/23600