Add type hints

[dyollb]

Is your feature request related to a problem? Please describe. ANTsPy currently doesn't use type hints.

• type hints help users understand what type of parameters are expected.
• type hints can be used by static type checkers to detect potential bugs, e.g. when you change a signature

Describe the solution you'd like

• I would offer to add type hints in most functions
• add an action to run mypy in the CI to ensure type hints are added and are still accurate

Describe alternatives you've considered Do nothing. Rely on pyright to guess the expected return types, and parameters (when there are defaults)

Additional context na