fix: implement exponential backoff for receipt polling

[pranavkonde]

fix: implement exponential backoff for receipt polling

Switches from fixed-interval to exponential backoff with jitter for receipt polling, improving efficiency and reliability.

Key Changes:

• Exponential backoff starts at 100ms (doubles each retry, max 10s, 5 retries)
• ±20% jitter to avoid synchronized retry spikes
• HTTP client timeout set to 30s
• Context-aware cancellation support
• Proper response body cleanup
• Improved error handling

Config:

• Initial backoff: 100ms (±20ms)
• Max backoff: 10s
• Max retries: 5
• HTTP timeout: 30s

Benefits:

• Reduces unnecessary requests and server load
• Handles failures and slow responses more gracefully
• Resource-safe and cancellation-friendly

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