Allow parsing a LUT from a memory buffer rather than a file

OCIO's LUT file parsing is set up to work from files on disk. It would be very helpful to be able to have a function that would take a memory buffer and use the LUT parsers to turn it into a GroupTransform.

There is a way to do this already using the recent ConfigIOProxy class. However, it takes a fair amount of code and a fair amount of OCIO expertise to write it. This task is to write that code and turn it into a parseFromBuffer method on the GroupTransform class.

The unit tests for ConfigIOProxy in Config_tests.cpp provide some good sample code that could be used as a starting point.

Beginne mit den Unit-Tests für ConfigIOProxy in Config_tests.cpp und verfolge anschließend, wie GroupTransform derzeit die LUT-Parser für Dateien verwendet. Implementiere und stelle GroupTransform::parseFromBuffer über den bestehenden pufferbasierten Ansatz bereit und füge Testabdeckung hinzu, die zeigt, dass eine LUT aus einem Speicherpuffer die erwartete GroupTransform erzeugt.

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