fix: prevent duplicate reasoning-end events in Ollama stream

[bishwajitcadhikary]

Description

This PR fixes an issue where the Ollama stream handler would repeatedly emit ThinkingCompleteEvent (mapping to reasoning-end) for every chunk after a reasoning block had finished.

The Problem:
The Stream handler checks if ($this->state->hasThinkingStarted()) to determine if it should emit a ThinkingCompleteEvent. However, the StreamState class lacked a method to reset thinkingStarted to false. As a result, once asking for reasoning began, the flag remained true for the duration of the stream, causing ThinkingCompleteEvent to be yielded for every subsequent data chunk that didn't contain a thinking delta.

The Fix:

1. Added markThinkingCompleted() to StreamState to allow resetting the thinkingStarted flag.
2. Updated Providers\Ollama\Handlers\Stream to call $this->state->markThinkingCompleted() immediately before yielding ThinkingCompleteEvent.

This ensures the event is emitted exactly once per reasoning block, preventing frontend errors (such as AI_UIMessageStreamError: Received reasoning-end for missing reasoning part) caused by duplicate end events.

Breaking Changes

None. This is a bug fix that adds a method to StreamState and corrects internal state management logic.