Fix tlv8 missing setuptools build dependency

tlv8 (pulled in by pynostr) is sdist-only and uses setuptools without
declaring it, breaking uv2nix build isolation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

flake.nix

@@ -58,6 +58,11 @@
             lib.composeManyExtensions [
               pyproject-build-systems.overlays.wheel
               overlay
+              (final: prev: {
+                tlv8 = prev.tlv8.overrideAttrs (old: {
+                  nativeBuildInputs = (old.nativeBuildInputs or [ ]) ++ [ final.setuptools ];
+                });
+              })
             ]
           )
       );