Avoid allocations when looking for trackers

Now we delay allocating owning `NameAndLocation` instances until
we construct a new tracker (because a tracker's lifetime can be
significantly different from the underlying tracked-thing's name).

This saves 4239 allocations (436948 -> 432709) when running
`./tests/SelfTest -o /dev/null`, at some cost to code clarity
due to introducing a new ref type, `NameAndLocationRef`.

0 files changed, 0 insertions, 0 deletions