fix: Token order during streaming

[charles-marion]

Issue #, if available:
#501

Description of changes:
Fixes two issues:

• Only shows a token if the previous ones are available (so it only adds the words at the end)
• Fix token missed. This happens when receiving 2 tokens in parallel. The fix is to move the reference of lastMessage.tokens out of updateMessageHistoryRef (so it uses the same array)

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Fix.streaming.mov

[bigadsoleiman]

LGTM.

Thanks for this long awaited fix