fix: prevent AudioContext and MediaStream memory leaks in Sampler widget

[WillyEverGreen]

Summary

This PR fixes a resource leak in the Sampler widget’s pitch detection feature.
When users start pitch detection and then close the widget, the microphone, AudioContext, and animation loop were not properly cleaned up.

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Problem

The startPitchDetection function in js/widgets/sampler.js had multiple resource-management issues:

1. Microphone Never Stopped (Privacy Concern)

Calling navigator.mediaDevices.getUserMedia({ audio: true }) activates the microphone, but the associated MediaStream tracks were never stopped when the widget closed. This resulted in:

• The browser microphone indicator remaining active
• Audio capture continuing after the widget was closed
• Unnecessary battery drain on laptops and mobile devices

2. AudioContext Never Closed

Each pitch detection session created a new AudioContext that was never closed. This caused:

• Accumulation of active AudioContexts
• Hitting browser AudioContext limits after repeated use
• Increased memory usage and eventual audio failures

3. Animation Loop Ran Indefinitely

The requestAnimationFrame(updatePitch) loop had no exit condition:

• The loop continued running even after the widget was closed
• CPU cycles were wasted on pitch calculations for an inactive widget
• Risk of errors when attempting to update removed DOM elements

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Solution

This PR adds explicit lifecycle management for pitch detection by tracking and cleaning up all related resources.

Added Resource Tracking

this.pitchDetectionAudioContext = null;
this.pitchDetectionStream = null;
this.pitchDetectionAnimationId = null;
this.isPitchDetectionRunning = false;

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.