Show test time with [mix amrita --trace] as similar way as ExUnit.

Hi. I'm interested in the issue #49 (Progress formatter captures and prints the slowest 10 tests), and I was playing around it.  As for the first step, how do you think about having [mix amrita --trace] as similar way as [mix test --trace]?
It's updated for success and failure tasks.

```Shell
% mix amrita --trace
test/integration/t_scoping.exs:5: unused import Support
test/integration/t_scoping.exs:12: this clause cannot match because a previous clause at line 7 always matches

Elixir.Integration.AsyncFacts
  testing async (0.00ms)

Elixir.CheckerFacts
  converting predicates into strings 
    arity 1 renders just predicate (0.00ms)
    atom argument is rendered (0.01ms)
    nil argument is rendered (0.00ms)
    string argument is rendered (3.2ms)
  converts negated predicates into strings 
....
```