Experimental REPL for debug purposes

[zippy]

PR summary

Adds a -r flag which starts a repl. Current commands are:

• help
• dump
• get <instance-name> <hash>
• chk

and the EAVI is now also included in state the dump.

Also fixes some critical bugs:

• holding and sending timed out direct messages after sim2h disconnect and reconnect.
• regeneration of LinkRemove aspects from eavi was creating incorrect aspects which set up mismatches between conductor and sim2h as they hashed to different values.
• fixed incorrect timestamp being used in EAVI for remove link entries
• validation was unnecessarily run twice when holding an add_link or a remove_link

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