lib.makeOverridable: fix functionArgs on returned function

[roberth]

Description of changes

Make makeOverridable transparent to function argument introspection, as one might expect it to be.

Should make arion's compatibility logic work again

• You're using a version of Nixpkgs that doesn't support the includeStorePaths parameter in d hercules-ci/arion#217 (comment)
• enables functionArgs on many other functions, such as the fetchers.

Draft to see if performance isn't overly affected by this - might consider ad hoc alternative, although it'd have to be really bad if we're going to reject a bugfix for performance reasons.
Correction: draft because of usual lib due diligence.
0.2% performance cost is worth it for correctness in many places.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.