Add self-test query for device-specific health checks

[polymerizedsage]

This adds a self-test query that can be used to return data about hardware calibration and health. An example test this query might be used for is validating a probe has all the correct register settings when it boots up.

The query message itself includes an optional field for specific electrode IDs to be used by self-tests that are conducted on specific electrodes. The response message (SelfTestResponse) contains a bool that is true if all tests passed. It then contains a list of SelfTestItem messages for each test procedure that was conducted. The SelfTestItem contains the name of the test, a boolean representing if the test passed, and a test_data field for more detailed data that the test may have collected. Finally, the test_report string can contain a message describing what went wrong if the test item fails.

I kept the definition of this query intentionally broad and flexible since it is meant to be used to return hardware-specific data that may not be standardized between probes.