Restructure Roles as a prepration for integration tests

[jbesraa]

This is the first stage of #1120

While trying to add integration tests we noticed that the roles logic should have a bit of refactor, mainly moving some of the library logic out of main.rs to lib folder/file in order to make it nicely accessible via testing.

Currently we have four different roles we want to refactor

• Translator - Move TranslatorSv2 lib code out of main.rs #1092
• JDServer - Move JDServer lib code out of main.rs #1095
• JDClient - Add JobDeclaratorClient struct #993
• Pool - MovePoolSv2 lib code out of main.rs #1097
• MiningDevice - Separate lib code from bin in mining-device #1163

Example for such change covering the Translator role https://github.com/stratum-mining/stratum/pull/1092/files

Goals:

• Get the roles code structured in a way that they can be composable inside the new integration test framework.
• Avoid breaking current behavior of roles. After this refactoring, it’s important that all roles continue passing the current MG test stack, and can also be launched manually while following the expected behavior.

[jbesraa]

Added MiningDevice to the list above and a corresponding PR

Edit: not sure if it should be part of this list actually