Generate reasonable expected schemata for Cache tables

Summary:
Ref T1191. Notable:

  - Rename `blob` to `bytes` for clarity.
  - Introduce raw schema specs.

Test Plan: See screenshots.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10501