v0.22.2

Added

• Borrowing history access: Memory::with_messages runs a visitor
  closure over the stored messages without handing out an owned copy. It is
  default-implemented in terms of get_messages (one full clone), so
  existing Memory implementors keep compiling unchanged;
  SlidingWindowMemory and TokenWindowMemory override it to borrow their
  storage under the lock, and TieredMemory forwards to its conversation
  sub-memory, so read-only consumers (serializing history to disk, measuring
  it, rendering it) no longer pay an O(history) deep copy per call.
  ErasedMemory::with_messages_erased is the object-safe counterpart
  (callers return values by writing into captured locals), also
  default-implemented, and routed through Memory::with_messages by the
  blanket impl so overriding backends keep their no-clone path through
  SharedMemory. SummaryMemory, SqliteMemory, and RedisMemory
  deliberately stay on the default: their get_messages composes or
  performs IO rather than returning a copy of borrowed storage. Additive
  only — no existing API changes.