Add benchmarking for `MR::FakeRecord`

This adds benchmarking for the `FakeRecord` mixin. This will
allow determining if a change affects the performance of the
`FakeRecord` mixin. This is to help keep test suites as fast as
possible.
Merge pull request #146 from redding/jcr-bench-fake-record

Add benchmarking for `MR::FakeRecord`