This line is not covered by tests:
https://github.com/JuliaOpt/SumOfSquares.jl/blob/b24d88e7e5dc2d848a7ee974b15697f421ee814e/src/copositive_inner_variable_bridge.jl#L45
as evidenced by jump-dev/SumOfSquares.jl#96

jldoctests are tested when building the documentation with Documenter.jl. This should be favored to @example or its friends.

a user might want to represent and evaluate multiple polynomials (different coefficients) with the same properties.
This is useful e.g. for gradients (= partial derivative polynomial for each dimension)!
add support for 2D coefficient arrays and adjust Numba jit compilation.
then the gradient can be returned as a single polynomial with the same exponents but 2D coefficients or multiple distinct