Function createFetch

Creates a fetch function with consistent promise resolution/rejection behavior.

Wraps a fetch function to provide consistent, sensible promise semantics where successful responses resolve and all errors reject with structured Problem exceptions:

• Response is ok (2xx status): Promise resolves with the response unchanged
• Response is not ok (non-2xx status): Response body is read according to Content-Type, converted to Problem, and promise rejects:
  • text/plain: Response body as text in report field
  • JSON-based MIME types (e.g., application/json, application/ld+json, application/problem+json): Parsed JSON payload in report field
  • Other content types: status code and statusText only
• Fetch exception occurs (network errors, timeouts, CORS failures): Exception is converted to Problem with status 0 and promise rejects

If response body parsing fails, promise rejects with Problem containing the original response status and statusText.