closeFor static method
Closes and forgets the instance owning storagePath, if there is one.
Note this keys on a storage PATH, unlike the same-named
AtPersistenceFactory.closeFor, which keys on an atSign.
Close BEFORE deleting the directory, not after: a path whose directory
has already been removed can only be matched lexically, which will not
find an instance filed under its resolved location. closeAll is immune,
since it works from the keys already in the map.
Implementation
static Future<void> closeFor(String storagePath) =>
_closeKey(canonicalPathFor(storagePath, create: false));