actually can't really beat multihash

oh well

iroh-car doesn't check them!!!!!!!!!!!!!!!!!!!!!!

https://github.com/n0-computer/iroh-car/issues/16

yay we're back to the old api (doctests pass again!!)

try to put the data into a more walk-friendly shape

oops it made things slower

benches:
huge: +0.36% (within noise margin)
midsize: +3.3%
little: +3.7%
tiny: +4.6%
empty: +6.4%

and hashbrowns

looks like another 7% improvement for ~free (allocator joke)

pretty good speedup!

with regression test and benchmark

conserve memory (unless something indicates that raising this would be useful)

it was *okay* in drop since we were dropping in spawn_blocking tasks, but kind of setting things up for problems later.

also all the option stuff to let it be take()n was gross and now it's gone

not generic over storage anymore, yay

seems like it's good on the write side

unclear if there's a win on reads