[Fix] SeanetResnetBlock.reset_state doesn't reset StreamingAdd, breaking multi-call decode (#407)

[yushuosun]

Motivation

In moshi_mlx, repeated streaming decode calls produce corrupted output because SeanetResnetBlock.reset_state() does not reset the block's StreamingAdd (#407).

Root cause

SeanetResnetBlock.reset_state() resets the shortcut and the sub-blocks:

def reset_state(self):
    if self.shortcut is not None:
        self.shortcut.reset_state()
    for b in self.block:
        b.reset_state()

but never resets self.streaming_add. StreamingAdd carries _lhs/_rhs residual buffers across step() calls, so after the first streaming decode those stale buffers leak into the next decode, corrupting the result.

Modifications

moshi_mlx/moshi_mlx/modules/seanet.py: add a reset_state() method to StreamingAdd (clears _lhs/_rhs) and call it from SeanetResnetBlock.reset_state(), consistent with how the block resets its other stateful submodules.

Duplicate-check

• Track A — gh api 'repos/kyutai-labs/moshi/pulls?state=open&per_page=100' --paginate grepped for 407 → no open PR references it.
• Track B — issue SeanetResnetBlock.reset_state() does not reset StreamingAdd buffers, breaking multi-call decode_step #407 has no in-progress claim.

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