Finds a .insider/ directory by walking upward from dir, or creates one
at dir when create = TRUE. The store is designed for explicit,
single-user curation; concurrent writers are not coordinated.
Examples
proj <- tempfile("proj-")
dir.create(proj)
store <- insider_store(proj, create = TRUE)
store
#>
#> ── insideR store ───────────────────────────────────────────────────────────────
#> Store root: /tmp/Rtmpvw2GbA/proj-180e622ff3a4/.insider
#> Project root: /tmp/Rtmpvw2GbA/proj-180e622ff3a4
#> Entries: 0
#> Kinds: none