move stateful checks (e.g. is_visium, is_single) higher up in the validator to avoid potential state-related issues

[ejmolinelli]

Motivation

The Validator object is stateful, and there are various points in the life of a validator object when a state might be set during validation. The states should be defined as early as possible and in a single place to avoid potential complications.

An example pointed out here

Definition of Done

the Validator state property setter functions are called once and only once (not counting after Validator.reset().

Tasks

Detail the specific tasks that can be used to accomplish the desired changes.
If detailed steps cannot be provided at this time, please file a Tech Proposal instead.

• cull state proeprty setters into a new or existing function
• call this function early in Validator life cycle
• remove all other property setter calls.
• state should be recomputed after adata is reassigned.

Extra Credit

• Extend more formal object properties with @property and @property.setter decorators (already used for Validator.adata)