What is the problem?

Custom metrics cannot be passed to different tasks or actors because its tags are not pickleable.

We should support passing metrics to tasks or other actors.

Reproduction (REQUIRED)

Please provide a script that can be run to reproduce the issue. The script should have no external library dependencies (i.e., use fake or mock data / environments):

If we cannot run your script, we cannot fix your issue.

• I have verified my script runs in a clean environment and reproduces the issue.
• I have verified the issue also occurs with the latest wheels.