[Feature] 支持流式读取

类似这样

```python
with open("a.wav", "rb") as f1, open("b.silk", "wb") as f2:
    encode_stream(f1, f2)
```

或者这样

```python
with Encoder("a.wav") as enc, open("b.silk", "wb") as f2:
    for packet in enc.encode_stream:
        f2.write(enc)
```