Ensure query only allows access to entries in holding list

[willemolding]

PR summary

Follow on from #1876

Using the traits introduced above there is a single place we can add management of the DHT holding list. It is now self managing and the mark_entry_as_held can be made private.

Entries added to the DHT are now added to the holding list automatically and reads will return None if an entry is not in the holding list rather than checking the CAS. This means less CAS reads and less chance of leaking private entries!

changelog

• [x] 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

• [x] this code has been documented according to our docs checklist

[zippy]

Hey @willemolding, the PR is going to need to be harmonized with the work we've done over here in: https://github.com/holochain/holochain-rust/pull/1904