fix mel_spectrogram cache keys to include all config parameters

[zhuxiaoxuhit]

The mel_basis and hann_window caches in mel_spectrogram use incomplete keys:

• mel_basis only keys on fmax + device, ignoring n_fft, num_mels, sampling_rate, fmin
• hann_window only keys on device, ignoring win_size

Two concrete failure modes:

1. A call with the same fmax but different num_mels silently returns the wrong mel filterbank.
2. A call with a different win_size hits a cached window of the wrong length and crashes in torch.stft with "Expected a window of size N, but got M".

There's also a coupling bug: both caches were populated under a single mel_basis check, so changing fmax between calls could silently overwrite hann_window with a different win_size.

Fix: use fully qualified independent keys for each cache so different configurations don't interfere with each other.