Unify PortableReference into HolonReference

[evomimic]

When shipping references to staged and saved holons back and forth between client and guest, we introduced a PortableReference data type. This enhancement makes some adjustments to StagedReference and SmartReference to allow HolonReference to be used as a portable reference type and eliminate the need for a separate PortableReference structure.

Currently SmartReference and StagedReference includes keys, but there doesn't seem to be a compelling reason for that. Their underlying holons provide access to their keys viaget_key methods.This enhancement drops key fields from both.

Proposal

• [x] Drop the key field and rc_holon fields from the definition of SmartReference
• [x] Clean up references to the key field in constructors/builders
• [x] Adjust implementations so that attempts to retrieve rc_holon from a SmartReference are delegated to get_rc_holon calls on the cache. The ensure_rc_holon function can be dropped. Calls an ensure_rc_holon should be replaced with calls on the cache_manager's get_rc_holon -- as should any attempts to access the SmartReference's (now-deleted) rc_holon field directly.
• [x] Drop the key field from the definition of StagedReference
• [x] Clean up references to the key field in constructors/builders
• [x] Replace uses of PortableReference with HolonReference

Testing

Ensure no loss of existing functionality by running regression tests:

• [ ] Ensure dance_test fixtures are setting the key field manually on all "Book" holons (but not "Person" holons) they are including in a test case

Definition of Done

• [ ] All sweetests pass

[dauphin3]

@evomimic there is no way to set the key in the stage_new_holon dance and therefore unable to match on expected from responsebody.staging_area

how best to proceed for implementing set_key_manually in tests?

should we add an optional parameter: key in RequestBody::ParameterValues ?

[evomimic]

When you create a holon in the dance_fixture, you can call the set_key_manually method to set the key on the holon.