R1:156b156e77b6

Give Conduit params/return/errors protected visibility

Summary:
Ref T7803. Ref T5873. I want to drive Conduit through more shared infrastructure, but can't currently add parameters automatically.

Put a `getX()` around the `defineX()` methods so the parent can provide default behaviors.

Also like 60% of methods don't define any special error types; don't require them to implement this method. I want to move away from this in general.

Test Plan:
- Ran `arc unit --everything`.
- Called `conduit.query`.