feat: add `to_dict`/`from_dict` to `StreamingChunk`

[sjrl]

Is your feature request related to a problem? Please describe.
Follow up from #9543

Currently, StreamingChunk is the only dataclass that does not support serialization and deserialization. This could create a potential failure if this dataclass is used as inputs to breakpoints, which rely on schema utility functions to serialize and deserialize component inputs.

However, currently none of our components return StreamingChunks as output so it's unlikely that this will cause issues with the pipeline breakpoints feature.

Relevant discussion: Comment by @sjrl on PR #9526

Solution you'd like
Add proper to_dict and from_dict methods to StreamingChunk.