AGC improvements for LocalMicrophoneDriver

[s-ilent]

Changes:

• Add a noise floor to AGC. When the mic is inactive, the AGC update is skipped, preventing it from automatically increasing the gain correction when the user stop talking.
• Added a hold timer to AGC. Reduces gain immediately when audio peaks (attack). If the volume is low, it waits for a 0.4s cooldown (hold) before gradually increasing the gain again (release).
• Only process a small portion of the incoming sound buffer, rather than the entire buffer. With a buffer the size of the sample rate, AGC would take 1 second to update. By performing AGC on a smaller chunk, the changes can take effect much faster.
• This change also updates denoising to use the smaller buffer.
• RollingRMS was corrected to not average the values directly (which is incorrect as RMS is a non-linear scale) and instead average the power/mean square before taking the sqrt.