Fix named camera spaces

[AlexeySmolenchuk]

Description

• Fixed "camera", "screen", "NDC", and "raster" transformation spaces.
• Moved them to named spaces and fetch on the Optix side.
• Fixed camera FOV. Here are the before/after results for 90°.
  
• The code was implying that the FOV is horizontal...

void
SimpleRaytracer::camera_params(const Matrix44& world_to_camera,
                               ustringhash projection, float hfov, float hither,
                               float yon, int xres, int yres)
{
    m_world_to_camera  = world_to_camera;
    m_projection       = projection;
    m_fov              = hfov;

...but implemented as vertical

    float k    = OIIO::fast_tan(fov * float(M_PI / 360));
    cx         = right * (xres * k / yres);
    cy         = (cx.cross(dir)).normalize() * k;

• Switched Optix texture to the cached version of ImageBuff

Tests

Most of the tests with testrender will fail because of the FOV fix and reinterpretation, but I can recalculate FOV in .xml scenes to make them look similar to previous results. It won't be a perfect match and would require updating ref images anyway.

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  fixed any problems reported by the clang-format CI test.