Create test utils module for unit tests

Currently, we have rib-base-test that contains espresso/instrumentation test dependencies.
We need to create a module that contains utility classes that can be used in local unit tests.

For example, see TestNode.kt
Also, we can add test implementations of `Rib.Dependency` dependencies

Start by examining rib-base-test and the TestNode.kt example to understand which utilities currently support tests and which dependencies require test implementations. Define the new local-unit-test utility module around those needs, including suitable Rib.Dependency implementations. Done means local unit tests can use the shared utilities without relying on espresso or instrumentation dependencies.

Written by the indexing model from the issue text.