fix(sdk): reset skipToTurnComplete when a new chat turn starts (#4744)

## ✅ Checklist

- [x] I have followed every step in the [contributing
guide](https://github.com/triggerdotdev/trigger.dev/blob/main/CONTRIBUTING.md)
- [x] The PR title follows the convention.
- [x] I ran and tested the code works

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## Testing

Reproduced with `useTriggerChatTransport` + `useChat` and the stop
pattern from the ai-chat frontend docs:

1. Send a message so a turn is streaming.
2. Call `transport.stopGeneration(chatId)`, then `useChat`'s `stop()`.
3. Send another message.

Before this change the second turn never renders: no parts arrive,
`status` stays `streaming`, and the session stays `isStreaming: true`,
so a stop button stays on screen until the page is reloaded. The run
itself is fine and everything persists, so a reload shows the full
response.

Cause: `stopGeneration` sets `state.skipToTurnComplete = true`, and the
read loop only clears that when it sees a `TURN_COMPLETE` record. The
abort closes the reader before that record arrives, so the flag survives
into the next turn and every record of that turn is skipped, including
its own `TURN_COMPLETE`.

After this change the same sequence streams the second turn normally.
Verified against 4.5.11 and 4.5.12 (both affected) with the equivalent
patch applied to the built SDK.

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## Changelog

Reset `skipToTurnComplete` when a new chat turn or action is sent, so a
message sent after `stopGeneration` streams normally instead of leaving
the chat stuck in a streaming state.

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Co-authored-by: Devin AI <devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: nicktrn <55853254+nicktrn@users.noreply.github.com>