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Depending on the order some of the constructors get executed, instances of the
logger can end up with a null pointer for the runner. This led to a segfault
when calling TimePs() on that nullptr.

Here we fix this in two steps: first the logger takes a device pointer, which
in turn contains a pointer to the runner that will eventually be initialized.
Also fix up the logger to simply use 0 as a timestamp for log events before the
runner is there.