fix(viz): memory leak in missing techniques scheme

Description

There is a memleak per frame in our rendering system, in the runtime creation of missing techniques.

How to test it?

On Windows

• Launch sight_viewer with a debugger attached
• Put a breakpoint in libs/viz/scene3d/compositor/material_mgr_listener.cpp:75
• Enable the display of the axis (last button in the toolbar)
• The breakpoint should never be raised