Add Audio2Pitch plugin: real-time monophonic pitch detection

[eacevedo1]

Summary

Adds a new Audio2Pitch_projucer plugin that uses Essentia's Audio2Pitch
algorithm to perform real-time fundamental frequency (F0) detection on a
monophonic audio signal.

The plugin follows the same structure and visual style as the existing
RMS_projucer template.

What it does

• Detects pitch in Hz and a confidence score (0–1) on every audio block
• Uses Essentia's Audio2Pitch algorithm internally.
• Displays both values in a live UI updated at 30 Hz

Features added beyond the RMS template

• Averaging window dropdown — selectable display smoothing over
  Off / 50 ms / 100 ms / 250 ms / 500 ms / 1000 ms to stabilise the
  inherently noisy per-frame pitch estimates

Tested on

• macOS (AU format, Ableton Live)
• Essentia built from source (build_external/)
• JUCE via Projucer (Xcode export)

UI