Goal of this package

When you request buffer of size N from System.Buffers.MemoryPool<T> returns IMemoryOwner<T> which can hold Memory<T> at least N elements. That proves to be a problem in some scenarios like passing serialized data back to your users. You need to pass them one more field: actual length of data. This pool will always trim IMemory<T> to requested length. It will also provide a property with an access to underlying buffer.