[RLlib] Properly serialize and restore StateBufferConnector states for policy stashing

[gjoliver]

Why are these changes needed?

Related issue number

Checks

• [ ] I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• [ ] I've run scripts/format.sh to lint the changes in this PR.
• [ ] I've included any doc changes needed for https://docs.ray.io/en/master/.
• [ ] I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • [ ] Unit tests
  • [ ] Release tests
  • [ ] This PR is not tested :(

[gjoliver]

The PR seems to solve the problem with 100-policy test at least. I wonder if it still works with the old numbers. @gjoliver Can you confirm that?

yes, it works with original numbers. just very slow right now because we are doing a lot of unnecessary policy stashing. I will file a separate issue for that.

[gjoliver]

tests look good finally with and without the flag flip. gonna merge now. thanks.