This PR fixes a memory usage issue with MacOS Photos integration.
Prior to this fix, Duplicati would allow the Photos library to stream an unlimited amount of data. For large files this would require all resources to be kept fully in memory.
With this fix, the reader is limited to 8MB read-ahead, such that the maximum size of memory use is bounded by 8MBxReaders, where readers are default cores/2.
Additionally, this significantly reduces the memory allocation/deallocation in the C# layer when processing PhotoKit entries.
Kenneth Skovhede
657467e409