Refactor/mtimehx

[kylebaron]

Summary

The evdata object is a way to shuttle new dosing information from the model back to the mrgsolve simulation sequence.

We are adding a check_unique attribute that allows users to skip checking the modeled event history. This lets you schedule identical events if needed.

This PR also adds dose amt into the event history check; this allows users to schedule dosing events to the same compartment at the same time but with different dose amounts without tapping that check_unique attribute.

At this point, tests are only focused on the check_equal feature.

Tests are getting added to a special C++ test space; this space will be added to the drone make target so tests will get run with push to drone.

[kyleam]

Looks good. The new handling fits nicely into the current code.

As with gh-1125, conflict in inst/maintenance/unit-cpp/test-cpp.R is due to new tests here and new tests from gh-1131. Confirmed that make test-cpp passes when all tests from both sides are included.