Add option to make BufferReader blocking to wait for future data.

[andeaseme]

We often prefer to wait for requested data.

class BufferReader:
    def __init__(
        self,
        buffer: RWLockSortedDeque,
        source_reader_info: dict,
        stop_event: threading.Event,
        *,
        blocking=False,  # <----  Add this
        read_size=1,
        peek=False,
        strict_n=False,
        ignore_no_item_found=False,
    ):
        ...

reader = stream_buffer.mk_reader(blocking=True). #  <---- Allow this

also update AudioBufferReader in audiostream2py