fix: pass result of `shm.Prune()` through `Wraith.SHMPrune()`

chore: update to go 1.21

chore: return amount of pruned cells from `shm.prune()`

fix: build

chore: tweak structure

chore: switch to hacker docs theme for them dark modes

chore: update to go 1.20

chore: update CI

chore: docs tweaks

chore: we no longer need wraith.go in root

chore: tweak USAGE.md

chore: initial USAGE.md

chore: bump deps

chore: update garble in ci

chore: some updates