Run a single upgrade step in isolation: stage store to version index - 1
(so the handler sees a known input for every component) then run entries[index]'s
handler, taking the store from version index - 1 to index. The building block
for a per-upgrader test — construct a store at version index - 1, populate,
await this, then assert against the version index schema.
Run a single upgrade step in isolation: stage
storeto versionindex - 1(so the handler sees a known input for every component) then runentries[index]'s handler, taking the store from versionindex - 1toindex. The building block for a per-upgrader test — construct a store at versionindex - 1, populate,awaitthis, then assert against the versionindexschema.