[release] 0.54.0 - Check user for UA field & increase error visibility (#390)

### New Features
- added sdk_error_callback option to listen for unexpected exceptions
caught
   - new metrics *sdk_exceptions_count* + *events_successfully_sent*

### Improvements
- stricter typing on statsig user to only allow JSON serializable type
   - check user for any UA fields before using UA





>Included In This Release
>- cd1d723 kat-statsig
>   - error handling update (#389)
>- 708d001 sroyal-statsig
>   - Check User for UA Fields (#388)

Author: kat-statsig

statsig/version.py

@@ -1 +1 @@
-__version__ = '0.53.0'
+__version__ = '0.54.0'