TextToImage and StyleTransfer should return uri instead of base64 string.

[msluszniak]

Images returned by TextToImage are currently pass as base64 strings. This is not the most effective way of doing that. Instead, we can save the images on the native side and then pass uri to this image as a result of calling forward. Additionally, typedoc forforward in style transfer should be corrected as now it indicates that method returns base64 string, but it returns uri, see: https://github.com/software-mansion/react-native-executorch/blob/main/packages/react-native-executorch/src/modules/computer_vision/StyleTransferModule.ts#L49