Call wandb.finish when the tracker is destructed if wandb is in use (#191)

runs always show "crashed" on my wandb, despite finishing successfully.
"Crashed" indicates that wandb did not finish sending the "success"
signal to the server so the server believes the client was terminated
unexpectedly. Furthermore, wandb log is incomplete (last lines missing).

This PR adds a call to `wandb.finish` when the Tracker was destructed
(oftentimes when `trainer.fit` finished) so that signals are sent to the
server and a data sync is performed.

Without this change:
<img width="526" alt="image"
src="https://github.com/user-attachments/assets/869da24e-c5b8-415c-b15a-bb79c49f96ce"
/>

With this change:
<img width="548" alt="image"
src="https://github.com/user-attachments/assets/16f0a40d-ea3b-48ed-93a4-f40ee01cb7c6"
/>

verl/utils/tracking.py

@@ -57,6 +57,10 @@ class Tracking(object):
             if backend is None or default_backend in backend:
                 logger_instance.log(data=data, step=step)
 
+    def __del__(self):
+        if 'wandb' in self.logger:
+            self.logger['wandb'].finish(exit_code=0)
+
 
 class _MlflowLoggingAdapter: