add loudness_per_window method

[DBraun]

Hello, thanks for this project!

What do you think of this new feature:

# Get loudness per window (e.g., to analyze loudness over time)
lufs_per_window = loudness.loudness_per_window(audio, sr, window_duration_sec=0.5)
print(f"Windows: {lufs_per_window}")

# Calculate percentage above threshold
percentage_loud = (lufs_per_window > -30).mean() * 100
print(f"{percentage_loud:.1f}% of windows are above -30 LUFS")

[iver56]

Thanks for the appreciation, and for the PR. This definitely looks like a useful feature! Unfortunately, I haven't had sufficient time to look into this lately