use sig_realloc in method OP_make_set

[dcoudert]

Method OP_make_set was introduced in #38692 in file src/sage/groups/perm_gps/partn_ref/data_structures.pxd to add the method make_set to DisjointSet (i.e., the ability to add a new element to a disjoint set).

We improve the method by using sig_realloc rather than a combination of sig_malloc and memcpy. This requires some changes in methods OP_new and OP_dealloc.

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