fix(logging): improve JSON serialization and add wandb directory to gitignore

- Fix float32 serialization issue in unified logger metrics flushing
- Add jax.numpy import for proper type handling
- Add wandb/ directory to .gitignore to exclude temporary tracking files
- Tested wandb integration: metrics, artifacts, and local backup working correctly

.gitignore

@@ -2,6 +2,9 @@
 artifacts/*
 runs/*
 
+# Experiment tracking
+wandb/
+
 # Python-generated files
 __pycache__/
 *.py[oc]