Use 2% as default risk-free rate fallback

Author: MDUYN

investing_algorithm_framework/services/metrics/risk_free_rate.py

@@ -1,7 +1,7 @@
 import logging
 
-# Default US 10-year Treasury yield approximation (4%)
-DEFAULT_RISK_FREE_RATE = 0.04
+# Default US 10-year Treasury yield approximation (2%)
+DEFAULT_RISK_FREE_RATE = 0.02
 
 logger = logging.getLogger("investing_algorithm_framework")