Calculates the score vector for the profiled loglikelihood of the mixed effects model with respect to the parameterization in which the random effects covariance matrix is represented in its full form (not using the Cholesky factor).
Parameters:  params : MixedLMParams or arraylike


Returns:  The score vector, calculated at `params`. : 
Notes
The score vector that is returned is taken with respect to the parameterization in which cov_re is represented through its lower triangle (without taking the Cholesky square root).
The input, if provided as a MixedLMParams object, can be of any parameterization.