refactor(api): replace map[string]uint64 with api.StoreVersion for store version handling

pkg/api/store.go

@@ -0,0 +1,14 @@
+package api
+
+// StoreVersion records the highest processed database version for each Corrosion actor UUID.
+// A version can include changes that were superseded, so it does not guarantee that all data
+// through that version is available locally.
+type StoreVersion map[string]uint64
+
+// MergeMax keeps the highest observed version for each actor in other.
+// The receiver must be initialised before calling MergeMax.
+func (v StoreVersion) MergeMax(other StoreVersion) {
+	for actor, version := range other {
+		v[actor] = max(v[actor], version)
+	}
+}