Function validate_displacement 

pub fn validate_displacement(
    model: &Model,
    level: ValidationLevel,
    report: &mut ValidationReport,
)

Validate displacement-specific resources and geometry.

This function validates:

• Displacement2D texture resources (path, height, offset)
• DisplacementMesh geometry (normals, gradients, texture coordinates)

Validation is progressive based on level:

• Standard: Reference integrity, count matching
• Paranoid: Geometric correctness (unit normals, finite values)