Fix NumPy 2 doctest scalar compatibility

[david-hoffman]

Problem statement: current NumPy reprs make utility doctests fail under the GitHub Actions Python 3.10 matrix.

Desired behavior: the doctest suite passes without weakening the test command.

Acceptance criteria:

• python -m pytest --doctest-modules dphtools tests passes locally.
• Utility examples remain accurate for users.
• Runtime scalar behavior is normalized only where it matches documented return types.

Affected modules:

• dphtools/utils/init.py

Scientific/numerical assumptions: no numerical tolerance changes. This is scalar type and doctest-output compatibility work.