Cursor and transactional support for CAS and EAV

[struktured]

PR summary

• Introduce CursorProvider, Cursor, and PersistenceManager traits
• make holochain-persistence-lmdb have full support for cursors
  • internal write cursors are lazy
  • ephemeral databases are internally maintained to stage diffs to the cas/eav
  • ability to commit or abort the stage diffs on the primary database
• Adds dynamic versions of the above so the Cursor, Eav, Ca associated types aren't required by users of the api

TODO

• Ensure store still doubles it size when necessary (ensure existing unit tests for it are sound)
• Implement persistence manager for other non lmdb persistence impls (should be trivial if we make them non transactional).
• Fix commented out transactional tomb stone test (doesn't compile)
• make creation of temporary database lazy
• remove 'static requirements in CursorDyn related apis.

Review checklist

• The story has unit or integration tests
• No new bugs, and any tech-debt is identified and justified
• There is enough API documentation (how to use)
• There is enough code documentation (how the code works)

[StaticallyTypedAnxiety]

Just popped in for a question, I was wondering how it handles tombstones.

[struktured]

Ashanti- the abstraction sits outside of this api in the `Attribute` enum. The idea in practice is the user of a cursor would do any CRUD related stuff in a transaction over the CAS and EAV together as they saw fit.

…

On Tue, Jan 14, 2020 at 1:45 AM Purple Hair Rust Bard < ***@***.***> wrote: Just popped in for a question, I was wondering how it handles tombstones. — You are receiving this because you were assigned. Reply to this email directly, view it on GitHub <#18?email_source=notifications&email_token=ABGTLIVRPHAA45XSHFD4W63Q5VNQJA5CNFSM4KFL3FVKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEI3PXWA#issuecomment-574028760>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABGTLIXA3NGBTKANKODDYKDQ5VNQJANCNFSM4KFL3FVA> .

[StaticallyTypedAnxiety]

Ashanti- the abstraction sits outside of this api in the Attribute enum. The idea in practice is the user of a cursor would do any CRUD related stuff in a transaction over the CAS and EAV together as they saw fit.
…
On Tue, Jan 14, 2020 at 1:45 AM Purple Hair Rust Bard < @.***> wrote: Just popped in for a question, I was wondering how it handles tombstones. — You are receiving this because you were assigned. Reply to this email directly, view it on GitHub <#18?email_source=notifications&email_token=ABGTLIVRPHAA45XSHFD4W63Q5VNQJA5CNFSM4KFL3FVKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEI3PXWA#issuecomment-574028760>, or unsubscribe https://github.com/notifications/unsubscribe-auth/ABGTLIXA3NGBTKANKODDYKDQ5VNQJANCNFSM4KFL3FVA .

Awesome! Looks good!

[timotree3]

these are incomplete comments but I'm posting them for the sake of our conversation