feat: rework GET retry logic with exponential backoff, jitter, and Retry-After support

[redmer]

Previously, transient GET failures retried at most three times after a fixed 60-second delay and only for transport errors.

GETs now retry up to 5 times on transient HTTP statuses (408/429/5xx) and connection errors, using exponential backoff with jitter and honoring the Retry-After header. Non-retryable 4xx responses raise immediately.

Changes:

• The retry_attempt kwarg of APIConnection.GET() was removed.
• Warnings and errors are now printed using the pyfwapi logger, not with print.
• Some exceptions are raised not as quickly, as pyfwapi will retry more consistently. They're still the same exceptions though.