Factor out error generation for function calls with wrong nargs.

[anntzer]

... matching the wording for standard functions.

Note that nargs_error returns the exception without raising it itself to
make the control flow clearer on the caller side.

PR Summary

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• New plotting related features are documented with examples.

Release Notes

• New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst

[ksunden]

Test for quiver nargs matches against that portion of the string, and thus must be updated

[anntzer]

oops, fixed, thanks.