drcachesim: add structured simulation results

This is a feature request to add an interface for retrieving simulation
results as structured data when using drcachesim as a library, to avoid
having to print out statistics and then parse them back in.

This will be immediately useful in the drcachesim_unit_tests.

Start by locating the drcachesim library entry points and drcachesim_unit_tests, then review how simulations currently print statistics. Done means the library exposes simulation results as structured data and the unit tests can retrieve them without parsing printed output.

Written by the indexing model from the issue text.