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I'm still scratching out prototypes in another directory to make it
easier to focus on the details I'm interested in rather than get
wrapped up with the kerfuffling details of the existing full
interfaces... as well as easier to try out different interfaces.
And at some point, of course, we want *codegen* for these things, while
what I'm plunking about with here is a sketch of the expected *output*.
So, this is a large step removed from the final code... but it's easier
to sketch this way and "imagine" where the templating can later appear.

This solution approach seems to be going largely well.

And we have some tests which count allocs very carefully to confirm
the desired result!

Still a lot to go.  There's large hunks of comments and unresolved
details still in this commit; I just need a checkpoint.

Some things around creation of maps are still looking tricky to
support optimizations for.  Research needed there.  A comment hunk
describes the questions, but so far there's no tradeoff-free answer.

Perhaps most usefully: here's also a checkpoint of the
"HACKME_memorylayout" document!  It also still has a few todos, but
it's the most comprehensive block of prose I've got in one place
so far.  Hopefully it will be useful reading for anyone else wanting
to get up to speed on the in-depth in "why" -- it's awfully,
awfully hard to infer this kind of thing from the eschatology of
just observing where pointers are in a finished product!
Signed-off-by: Eric Myhre <hash@exultant.us>