Use internal stack trace library in registry

This change is functionally a no-op. Instead of using the native traceback library, we use tf_stack.extract_stack() to get the frame we care about and tf_stack.convert_stack() to convert this to the same format.

This reduces the number of file posix.stat calls. In my example application, we reduce the time spent in register() by a factor of 15.

We also add a test to verify that we're extracting the same information.

PiperOrigin-RevId: 223142289