Adds COMFY_API_MAX_RETRIES, COMFY_API_RETRY_DELAY, and
COMFY_API_RETRY_BACKOFF environment variables that override the default
retry parameters for all API node HTTP requests (sync_op, sync_op_raw,
upload_file, download_url_to_bytesio).
Users in regions with unstable networks (e.g. behind the GFW in China)
can increase the retry budget to tolerate longer network interruptions:
COMFY_API_MAX_RETRIES=10 COMFY_API_RETRY_DELAY=2.0 python main.py
Defaults remain unchanged (3 retries, 1.0s delay, 2.0x backoff) when
the env vars are not set.
