Move dbtest proto bits into their own module.

**Describe the bug**

If we move the dbtest package into its own module, then we can remove some of the dev tooling dependencies from the `dbw` package.

Start by locating the dbtest package and the dbw module definition, then inspect how development-tooling dependencies are currently declared. Done means the dbtest proto bits have their own module and the dbw package no longer includes dependencies that are only needed by dbtest.

Written by the indexing model from the issue text.