Python buffer API refactoring, RTP Op Wrapper

[hunhoffe]

This PR cleans up some aspects of using buffers and also RTP writes in conjunction with buffers. Previously, the API could be used something like this (from the ml/bottleneck example):

rtpComputeTile5 = Buffer(ComputeTile5, [16], np.int32, "rtpComputeTile5")
...
NpuWriteRTPOp("rtpComputeTile2", index=0, value=1)  # scale

With the changes, these code snippets become:

rtpComputeTile2 = buffer(ComputeTile2, np.ndarray[(16,), np.dtype[np.int32]], "rtpComputeTile2", use_write_rtp=True)
...
rtpComputeTile2[0] = 1  # scale

I also cleaned up a few examples, for instance replacing a memref.alloc with a buffer and replacing the last lingering objectfifo_release() with the more object-oriented version.