Fix hold aspect bugs

[zippy]

PR summary

This PR fixes bugs in the conductor and sim2h with hold aspect:

• two conductor fixes during error cases (like base hasn't arrived yet) in hold_aspects request:
  • stop incorrectly recording aspects as held
  • stop locking up the future
• because sim2h doesn't get error messages from a hold_aspect request it must also not record aspects sent in those messages as held, and thus the conductor must explicitly send back a list of aspects held after a hold_aspect request

This fix requires putting in a holding attempt result into the state for the future to look for to be able to pass the result back, as well as making sure to be able to clean up that state data when the pending validation is cleared.

testing/benchmarking notes

( if any manual testing or benchmarking was/should be done, add notes and/or screenshots here )

followups

( any new tickets/concerns that were discovered or created during this work but aren't in scope for review here )

changelog

• if this is a code change that effects some consumer (e.g. zome developers) of holochain core, then it has been added to our between-release changelog with the format

- summary of change [PR#1234](https://github.com/holochain/holochain-rust/pull/1234)

documentation

• this code has been documented according to our docs checklist

[Connoropolous]

hey Eric,
I was reading this anyways and I get the sense things are a little sparse on the review side of things, so I figured I would lend a hand.