Alumna::MemorySessionStore
Inherits Alumna::SessionStore < Reference < Object
In-process session map. Use one instance per process (single backend). Swap for a Redis SessionStore to share sessions across processes.
Expiry uses Time.instant (monotonic). Cookie Max-Age uses wall clock.
No background fiber. Expired rows are dropped on get and by an amortized
prune every cleanup_every writes/reads, same as MemoryRateLimitStore.