Should allow assignment operatior for pitch_detector and signal_conditioner

[xconverge]

This should be valid syntax and allow assignment instead of returning an error:

cycfi::q::pitch_detector test;
test = cycfi::q::pitch_detector{lowest_frequency, highest_frequency, sample_rate, lin_to_db(0)};

Error currently:

error: use of deleted function 'cycfi::q::pitch_detector& cycfi::q::pitch_detector::operator=(const cycfi::q::pitch_detector&)'
   60 |                                   sample_rate, lin_to_db(0)};