nifgen methods that have "waveform handle" and "waveform name" should use fancy wrapper

[marcoskirsch]

For nifgen.Session.write_waveform, we created a Fancy Wrapper in which a parameter is either the waveform handle or the waveform name.

We found two instances that could and should do the same for consistency.

• set_waveform_next_write_position and set_named_waveform_next_write_position
• clear_arb_waveform and delete_named_waveform

The next_write_position methods are very niche, so we could just stop code-generating until a compelling use case arises. If that happens, we should make sure it's tracked via an issue.