DEV: Add a new way to run specs in parallel with better output (#7778)

* DEV: Add a new way to run specs in parallel with better output

This commit:

 1. adds a new executable, `bin/interleaved_rspec` which works much like
    `rspec`, but runs the tests in parallel.

 2. adds a rake task, `rake interleaved:spec` which runs the whole test
    suite.

 3. makes autospec use this new wrapper by default. You can disable this
    by running `PARALLEL_SPEC=0 rake autospec`.

It works much like the `parallel_tests` gem (and relies on it), but
makes each subprocess use a machine-readable formatter and parses this
output in order to provide a better overall summary.

(It's called interleaved, because parallel was taken and naming is
hard).

* Make popen3 invocation safer

* Use FileUtils instead of shelling out

* DRY up reporter

* Moved summary logic into Reporter

* s/interleaved/turbo/g

* Move Reporter into its own file

* Moved run into its own class

* Moved Runner into its own file

* Move JsonRowsFormatter under TurboTests

* Join on threads at the end

* Acted on feedback from eviltrout

lib/turbo_tests.rb

@@ -0,0 +1,62 @@
+require 'open3'
+require 'fileutils'
+require 'json'
+require 'rspec'
+require 'rails'
+
+require 'parallel_tests'
+require 'parallel_tests/rspec/runner'
+
+require './lib/turbo_tests/reporter'
+require './lib/turbo_tests/runner'
+require './lib/turbo_tests/json_rows_formatter'
+
+module TurboTests
+  FakeException = Struct.new(:backtrace, :message, :cause)
+  class FakeException
+    def self.from_obj(obj)
+      if obj
+        obj = obj.symbolize_keys
+        new(
+          obj[:backtrace],
+          obj[:message],
+          obj[:cause]
+        )
+      end
+    end
+  end
+
+  FakeExecutionResult = Struct.new(:example_skipped?, :pending_message, :status, :pending_fixed?, :exception)
+  class FakeExecutionResult
+    def self.from_obj(obj)
+      obj = obj.symbolize_keys
+      new(
+        obj[:example_skipped?],
+        obj[:pending_message],
+        obj[:status].to_sym,
+        obj[:pending_fixed?],
+        FakeException.from_obj(obj[:exception])
+      )
+    end
+  end
+
+  FakeExample = Struct.new(:execution_result, :location, :full_description, :metadata, :location_rerun_argument)
+  class FakeExample
+    def self.from_obj(obj)
+      obj = obj.symbolize_keys
+      new(
+        FakeExecutionResult.from_obj(obj[:execution_result]),
+        obj[:location],
+        obj[:full_description],
+        obj[:metadata].symbolize_keys,
+        obj[:location_rerun_argument],
+      )
+    end
+
+    def notification
+      RSpec::Core::Notifications::ExampleNotification.for(
+        self
+      )
+    end
+  end
+end