Revert "remove unused variable zbl_weight in DPZBLLinearEnergyAtomicModel"

This reverts commit 4932fbe.

Author: njzjz

deepmd/dpmodel/atomic_model/linear_atomic_model.py

@@ -509,6 +509,5 @@ def _compute_weight(
         coef = xp.where(right_mask, xp.zeros_like(coef), coef)
         # to handle masked atoms
         coef = xp.where(sigma != 0, coef, xp.zeros_like(coef))
-        # never used variable
-        # self.zbl_weight = coef
+        self.zbl_weight = coef
         return [1 - xp.expand_dims(coef, -1), xp.expand_dims(coef, -1)]