feat: SchemaRecord stage-1, never write a Model again

[runspired]

Its Happening.

(Note: no implementation here yet, just all the infra and the README). This PR will explore the final design for the associated RFCs (we expect a minimum of 3 RFCs to achieve this)

stage-1: feature compat with @ember-data/model
stage-2: feature compat with ModelFragments
stage-3: deeply nested inverse: null relationships
stage-4: deeply nested managed inverses, partial record support

TODO Stage 1:

• Implement Store and Cache forking for JSON:API Cache (already RFC'd)
• Implement Improved Schema Service (Map, simpler field defs, registerDerivation, registerTransform, addSchemas)
  • RFC Improved SchemaService
• Implement Paginated Collection Relationships
  • RFC Paginated Relationships
• Implement attribute, resource, collection behaviors
  • RFC SchemaRecord