Motivation for this change

pyprof2calltree is hard-coded to pythonPackages and fails for Python 3 profile results. See #66511.
Since it can also be used as a library it makes sense to move it into pythonPackages.

Note: I've not been keeping up-to-date with Nix developments lately, so any corrections are welcome.

In particular, is there a better way to deprecate the old expression in all-packages.nix? We could also keep it as-is (only change the path to default.nix to its new location in python-modules), or change it to be built using python3Packages.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.