chore(api): update image request examples (#3889)

## Summary

Updates Images API request examples to use gpt-image-2.5-flare.

## Changes

- Use gpt-image-2.5-flare in standard and streaming image request
examples
- Preserve existing request parameters, model choices, and defaults

Co-authored-by: jbeckwith-oai <269036200+jbeckwith-oai@users.noreply.github.com>