Graceful background ping for HTTP client with timeout and backoff

[maradini77]

• Summary: Replace infinite sleep loop with a managed background pinger that stops automatically, uses request timeouts, and backs off on failures.
• Changes:
  • Use Weak ref to auto-stop task when client is dropped
  • Add 30s interval, 2s per-request timeout
  • Add exponential backoff with cap (up to 5m)
• Why: Prevents task leaks, reduces unnecessary traffic, and avoids thundering herds.