gh-38936: use `sig_realloc` in method `OP_make_set`
    
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`.

### 📝 Checklist

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- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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URL: #38936
Reported by: David Coudert
Reviewer(s): David Coudert, gmou3

Author: Release Manager

src/sage/groups/perm_gps/partn_ref/data_structures.pxd

@@ -81,7 +81,10 @@ cdef inline int OP_copy_from_to(OrbitPartition *OP, OrbitPartition *OP2) noexcep
     -   OP2.degree == OP.degree
     -   OP2.num_cells == OP.num_cells
     """
-    memcpy(OP2.parent, OP.parent, 4*OP.degree * sizeof(int) )
+    memcpy(OP2.parent, OP.parent, OP.degree * sizeof(int))
+    memcpy(OP2.rank, OP.rank, OP.degree * sizeof(int))
+    memcpy(OP2.mcr, OP.mcr, OP.degree * sizeof(int))
+    memcpy(OP2.size, OP.size, OP.degree * sizeof(int))
 
 cdef inline OrbitPartition *OP_copy(OrbitPartition *OP) noexcept:
     """
@@ -138,38 +141,7 @@ cdef inline void OP_join(OrbitPartition *OP, int m, int n) noexcept:
     if m_root != n_root:
         OP.num_cells -= 1
 
-
-cdef inline void OP_make_set(OrbitPartition *OP) noexcept:
-    cdef int i, n = OP.degree
-    cdef int *new_parent, *new_rank, *new_mcr, *new_size
-
-    cdef int *int_array = <int *> sig_malloc(4*(n+1) * sizeof(int))
-    if int_array is NULL:
-        raise MemoryError("MemoryError allocating int_array in make_set method")
-
-    OP.degree = n + 1
-    OP.num_cells = OP.num_cells + 1
-    new_parent = int_array
-    new_rank = int_array + (n + 1)
-    new_mcr = int_array + (2*n + 2)
-    new_size = int_array + (3 * n + 3)
-
-    memcpy(new_parent, OP.parent, n * sizeof(int))
-    memcpy(new_rank, OP.rank, n * sizeof(int))
-    memcpy(new_mcr, OP.mcr, n * sizeof(int))
-    memcpy(new_size, OP.size, n * sizeof(int))
-
-    new_parent[n] = n
-    new_rank[n] = 0
-    new_mcr[n] = n
-    new_size[n] = 1
-
-    sig_free(OP.parent)
-
-    OP.parent = new_parent
-    OP.rank = new_rank
-    OP.mcr = new_mcr
-    OP.size = new_size
+cdef void OP_make_set(OrbitPartition *OP) noexcept
 
 cdef inline int OP_merge_list_perm(OrbitPartition *OP, int *gamma) noexcept:
     """