[SofaCUDA] FixedProjectiveConstraint: Fix for double templates

[fredroy]

Based on

• [SofaCUDA] Call register functions in the plugin initialization function #5961

Bug fixed by Claude 🤖

The beam was not fixed when switching to CudaVec3d.

CudaVec3f (OK)

CudaVec3d (Bug)

CudaVec3d (after PR, OK)

and added the scene with the cudavec3d example

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