[Bug] streamify is appending StatusStreamingCallback directly to the shared settings.callbacks list

[glesperance]

What happened?

Bug

streamify is appending StatusStreamingCallback directly to the shared settings.callbacks list.

That list is mutated in place and reused across calls, callbacks (and their status message providers) leaked between different dspy.streamify(...) invocations.

see https://github.com/stanfordnlp/dspy/blob/main/dspy/streaming/streamify.py#L164

Steps to reproduce

refer to the tests added in #9073 for steps to reproduce

DSPy version

3.0.3