Test suite hangs due to config loading before test environment setup

Bug Description

The test suite hangs or times out when running unit tests due to a configuration loading issue.

Root Cause

The tradingagents/config.py file calls get_config() at module import time (line 68), which validates API keys. However, the test fixture in tests/conftest.py sets test environment variables (lines 11-14) but imports DEFAULT_CONFIG afterwards (line 16). This creates a race condition where:

1. When pytest imports the test files, it loads conftest.py
2. conftest.py sets test environment variables
3. conftest.py then imports DEFAULT_CONFIG from tradingagents.default_config
4. This triggers the import of tradingagents.config, which immediately calls get_config()
5. The validation may fail or hang waiting for API keys

Impact

• Unit tests cannot run properly
• CI/CD pipeline failures
• Development workflow blocked

Solution

The config module should not eagerly load configuration at import time. Instead, it should use lazy loading or allow tests to override the configuration before validation occurs.

Steps to Reproduce

1. Run python -m pytest tests/unit/
2. Tests will hang or timeout

Environment

• Python 3.13
• pytest
• TradingAgents framework