Add auto sampling rate

[Blaizzy]

Most models now have custom sampling rate so we are deprecating the sampling-rate args for hard-coded ones provided by the creators.

You can access the sampling rate of any model by using the sample_rate property or importing the config.

from mlx_audio.tts.models.llama import Model, ModelConfig
config = ModelConfig()
model = Model(config)

print(model.sample_rate)

Note: You can still customize this by resampling the audio afterwards.

Closes #144