gangof4_plot(response) rejects precomputed responses with default options #1264

Title: gangof4_plot(response) rejects precomputed responses with default options

Problem

The documented gangof4_plot(response) call appears to fail when passed a precomputed Gang of Four response.

Minimal reproducer:

import control as ct

P = ct.tf([1], [1, 1])
C = ct.tf([2], [1])

response = ct.gangof4_response(P, C)
ct.gangof4_plot(response)

Expected: Plot the precomputed 2×2 frequency response.

Problem in current main: The frequency-option check treats the default Hz=False as an invalid override because False is not None evaluates to True. This forces a ValueError even when no frequency options were supplied.

There is also a separate argument-forwarding issue: the same branch calls response.plot(kwargs) instead of response.plot(**kwargs), passing the options dictionary as a positional argument.

Both issues are visible in control/freqplot.py. The control-flow condition has been checked independently; I have not executed the complete unmodified package locally.

Would you consider these bugs in the documented response-first API? If so, I can provide a focused fix and regression tests.

Related: #1261, following the request to discuss the behavior in an issue before submitting a PR.