Deprecate MemoryControlPlaneClient as pass-through to MemoryClient

MemoryControlPlaneClient and MemoryClient have significant functional
overlap. MemoryClient is a superset that provides all control plane
operations plus data plane features, response normalization, and typed
strategy helpers. Maintaining both creates a maintenance burden and user
confusion.

This refactors MemoryControlPlaneClient to be a thin pass-through that
delegates all operations to an internal MemoryClient instance, and emits
a DeprecationWarning on instantiation directing users to migrate.

Closes #247

Author: jariy17