Implement CoreMetrics

[adamgfraser]

The CoreMetrics service is designed to interface directly with package private methods in FiberContext within ZIO to expose metrics on the execution of ZIO programs. This ticket is to actually implement that service. This is dependent on functionality being added to ZIO to expose the needed functionality, which should hopefully be complete in advance of the hackathon. Assuming that is ready, implementing the service will consist primarily of calling those methods and re-exporting their results, along with adding tests to show that the functionality is working correctly.

[mtjon]

have these dependencies been added to ZIO core in time?

[atooni]

I ll have a go at this

[atooni]

I ll have a go at this

[adamgfraser]

This has been obviated by the move of diagnostics into ZIO Core.