micd.py: optimize processing with real FFT and cached hanning window

[deanlee]

This PR enhances performance in the micd processing code by:

1. Replaced the complex FFT (fft) with the real FFT (rfft), this changes Improved efficiency for real-valued audio data.
2. Caching the Hanning Window: Reduced computation overhead by precomputing and caching the window.

Changes:

1. Replaced np.fft.fft with np.fft.rfft.
2. Replaced np.fft.ifft with np.fft.irfft.
3. Cached the Hanning window used in apply_a_weighting. saving ~1.5 ms on every update.

These optimizations improve the speed and efficiency of micd processing. Simple tests using the htop tool show a 3-4% reduction in CPU usage.

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[sshane]

trigger-jenkins

[sshane]

Was ~4%

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