Update o3 prices

[mrubens]

https://platform.openai.com/docs/models/o3

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Important

Update o3, o3-high, and o3-low model prices in openai.ts to lower values.

• Pricing Update:
  • In openai.ts, updated inputPrice, outputPrice, and cacheReadsPrice for o3, o3-high, and o3-low models from 10.0, 40.0, and 2.5 to 2.0, 8.0, and 0.5 respectively.

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