[chore] refactor tests in `src/chainstate/stacks/miner.rs` into one or more files

[jcnelson]

Lots of these tests aren't really related to mining, but depend on test infrastructure in this file. They should be refactored, so that tests can live closer in the codebase to the code they test.

[jcnelson]

This is completed in next

[blockstack-devops]

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