Refactor wallet_tracker to stabilize Etherscan API, add DB pooling and retry logic

[cto-new]

Overview: Refactored wallet_tracker to stabilize Etherscan API handling, enable DB connection pooling, add a robust retry strategy, and validate configuration at startup. The changes ensure graceful shutdown, efficient DB usage, and clearer logging.

Details:

• Harden Etherscan API request handling with improved status processing and logging.
• Implement RetryStrategy with exponential backoff (max 3 retries, 2-10s; non-retry on invalid API key).
• Add PostgreSQL connection pooling (ThreadedConnectionPool) and reuse; preserve SQLite compatibility.
• Validate configuration at startup (ENV vars, format URLs, connectivity tests).
• Support graceful shutdown and work_mem context for large queries.
• Update tests and demos to cover new behavior.
• Wallet addresses configuration now via environment variables (WALLET_ADDRESSES and WALLET_ADDRESS) with fallback example.