Add BLEP-corrected hard sync

[TXBDan]

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Description

This adds hard oscillator sync support to the Oscillator class, intended for use in synthesis patches where a "master" oscillator resets a "slave" oscillator at each cycle — a classic analog synth technique (Moog, Minimoog, Korg Minilogue, etc.) that produces harmonically rich timbres when the slave is tuned above the master.

New API
void SyncReset(float frac) — resets the slave oscillator's phase with a polyBLEP correction to reduce aliasing at the discontinuity. frac is the sub-sample position (0..1) within the master's last processed sample at which the wrap occurred.

float GetEocFraction() const — returns the fractional wrap position after IsEOC() is true. Used to pass the sub-sample timing to the slave.

Usage

float m = master.Process();
if (master.IsEOC())
    slave.SyncReset(master.GetEocFraction());
float s = slave.Process();

Implementation notes
GetEocFraction() is inline; no library rebuild needed to use it.
SyncReset(float) lives in oscillator.cpp — requires a library rebuild.
The BLEP residual corrects the sample immediately after the sync event. The pre-sync sample cannot be corrected in an online implementation (causality limitation), consistent with the existing polyBLEP approach in this class.
NaiveWaveformValue() is a private helper that evaluates the unfiltered waveform at an arbitrary phase, used to compute the step magnitude at the sync discontinuity.
The built-in polyBLEP is suppressed for one sample after sync via skip_builtin_polyblep_, since its assumed step magnitude of 2 is incorrect for a sync event.

Testing

Verified sync waveforms using oscilloscope. I also compared with and without BLEP correction and observed the aliasing improvement visible on the oscilloscope and by ear.

Demos / Example Code

You can test a Korg Minilogue emulation on Daisy Pod hardware with this project: https://github.com/TXBDan/DaisyMinilogue