test: achieve 100% test coverage for core engine modules

[Cylae]

This PR introduces a comprehensive suite of unit tests across all core engine/ modules and ai/ logic to ensure strict stability and full path evaluation of all execution, fallback, and error branches.

Key enhancements:

• Achieved 100% Test Coverage for ai_wrapper, async_utils, ccxt_connector, db_manager, ib_connector, indicators, market_utils, notifier, portfolio_manager, and risk_manager.
• Excluded un-testable dashboard UI (app.py), abstract interfaces (base_connector.py), and the infinite execution loop (main.py) from coverage metrics via a newly configured .coveragerc.
• Added edge case tests for API rate limits, WebSocket disconnects, event loop state checks, database access exceptions, and JSON malformation limits.
• Ensured zero destructive testability by keeping robust aiohttp contexts, TTL caching, and pydantic-settings constructs perfectly intact through usage of unittest.mock.patch tools for environment mapping and event loop timing modifications.
• Implemented concurrent database write safety tests and restored graceful db.close() mapping in DatabaseManager.
• Regenerated and aligned the README.md tutorial with current infrastructure state and date values.

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PR created automatically by Jules for task 5028045365879075229 started by @Cylae

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