Remove deprecated Biquad and replace with BlockBiquad

[relic-se]

Fixes #10061

• Replace the deprecated synthio.Biquad with synthio.BlockBiquad (now named synthio.Biquad)
• Remove synthio.Synthesizer.low_pass_filter, synthio.Synthesizer.high_pass_filter, and synthio.Synthesizer.band_pass_filter
• Remove synthio.AnyBiquad from documentation
• Coefficients from biquad_filter_state have been moved into synthio_biquad (biquad_filter_state is still used for input and output state)

These updates have been tested on a Waveshare RP2040-PiZero with the Waveshare WM8960 Audio HAT. I can share test code if needed.

For interest: @dhalbert @gamblor21

[dhalbert]

This looks good to me but I'd appreciate testing and/or a look-over by a synthio user as well. Thanks.

[gamblor21]

I'll try to test it out soon. Did any existing learn guides about synthio refer to these? I think some did.