PBC GDF/CDERI corruption at CPU-GPU mapped-memory boundary on AMD CPU + NVIDIA GPU systems

## Description

I encountered this issue when running `UKS.py` for a defect-system calculation. With the same input settings, the first SCF step already gives different results on different machines.

### Wrong result

```text
E1 = -1886.2263122955874  Ecoul = 498.7505538078927  Exc = -362.2990524302787
init E= -2704.40328934829
cond(S) = 773470.6758133224

Correct result

E1 = -1886.2263122955874  Ecoul = 534.0687392940991  Exc = -364.5454736907426
init E= -2671.33152512255
cond(S) = 773470.6758133224

This bug later causes the gradients to blow up during geometry optimization.

Suspected Location

I traced the problem to the CPU-GPU boundary in the PBC density fitting code. In particular, the issue appears to be related to reading from or writing to CUDA mapped host memory.

Bug 1: gpu4pyscf/pbc/df/rsdf_builder.py

The original code uses:

libpbc.store_col_segment(
    cderi.ctypes,
    ctypes.cast(j3c.data.ptr, ctypes.c_void_p),
    ctypes.c_int(naux), ctypes.c_int(nao_pairs),
    ctypes.c_int(p0), ctypes.c_int(p1))

Changing it to a CPU-mediated copy fixes this part:

cderi[:, p0:p1] = j3c.get()

Bug 2: gpu4pyscf/pbc/df/df.py

The original code uses:

out = asarray(cderi_sparse[p0:p1])

Changing it to a safe host copy before transferring to GPU fixes this part:

out = cp.asarray(np.array(cderi_sparse[p0:p1], copy=True, order='C'))

Result After Workaround

After applying both changes, the SCF calculation gives the correct result.

E1 = -1886.2263122955874  Ecoul = 534.0687392940991  Exc = -364.5454736907426
init E= -2671.33152512255
cond(S) = 773470.6758133224

The cif file is

# generated using pymatgen
data_SiC62
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.13600000
_cell_length_b   7.13600000
_cell_length_c   7.13600000
_cell_angle_alpha   90.00000000
_cell_angle_beta   90.00000000
_cell_angle_gamma   90.00000000
_symmetry_Int_Tables_number   1
_chemical_formula_structural   SiC62
_chemical_formula_sum   'Si1 C62'
_cell_volume   363.38293146
_cell_formula_units_Z   1
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  C  C0  1  0.12294326  0.37534817  0.36906195  1
  C  C1  1  0.13041920  0.37928118  0.86958079  1
  C  C2  1  0.12341567  0.87764427  0.37266968  1
  C  C3  1  0.12690288  0.87883343  0.87309711  1
  C  C4  1  0.62805202  0.36111897  0.37194794  1
  C  C5  1  0.63093801  0.37534817  0.87705673  1
  C  C6  1  0.62386126  0.87278066  0.37613870  1
  C  C7  1  0.62733029  0.87764427  0.87658433  1
  C  C8  1  0.00157569  0.00157569  -0.00157569  1
  C  C9  1  0.00081094  0.00081094  0.49818735  1
  C  C10  1  0.00081094  0.50181265  -0.00081094  1
  C  C11  1  -0.00012198  0.50083957  0.49916043  1
  C  C12  1  0.50181265  0.00081094  -0.00081094  1
  C  C13  1  0.50083957  -0.00012198  0.49916043  1
  C  C14  1  0.50083957  0.50083957  0.00012198  1
  C  C15  1  0.12690288  0.12690288  0.12116656  1
  C  C16  1  0.13041920  0.13041920  0.62071879  1
  C  C17  1  0.12341567  0.62733029  0.12235572  1
  C  C18  1  0.12294326  0.63093801  0.62465180  1
  C  C19  1  0.62733029  0.12341567  0.12235572  1
  C  C20  1  0.63093801  0.12294326  0.62465180  1
  C  C21  1  0.62386126  0.62386126  0.12721934  1
  C  C22  1  0.62805202  0.62805202  0.63888100  1
  C  C23  1  -0.00068804  0.24966526  0.24641310  1
  C  C24  1  0.00413109  0.25310400  0.74689599  1
  C  C25  1  -0.00192854  0.75006920  0.24993078  1
  C  C26  1  -0.00068804  0.75358689  0.75033472  1
  C  C27  1  0.50160940  0.24606539  0.24596598  1
  C  C28  1  0.51585589  0.24889183  0.75110816  1
  C  C29  1  0.49767349  0.74654594  0.25345404  1
  C  C30  1  0.50160940  0.75403400  0.75393459  1
  C  C31  1  0.37621678  0.37621678  0.12287473  1
  C  C32  1  0.37524496  0.87625020  0.12374979  1
  C  C33  1  0.37621678  0.87712526  0.62378319  1
  C  C34  1  0.87625020  0.37524496  0.12374979  1
  C  C35  1  0.87712526  0.37621678  0.62378319  1
  C  C36  1  0.87544109  0.87544109  0.12455890  1
  C  C37  1  0.87625020  0.87625020  0.62475501  1
  C  C38  1  0.24966526  -0.00068804  0.24641310  1
  C  C39  1  0.25310400  0.00413109  0.74689599  1
  C  C40  1  0.24606539  0.50160940  0.24596598  1
  C  C41  1  0.24889183  0.51585589  0.75110816  1
  C  C42  1  0.75006920  -0.00192854  0.24993078  1
  C  C43  1  0.75358689  -0.00068804  0.75033472  1
  C  C44  1  0.74654594  0.49767349  0.25345404  1
  C  C45  1  0.75403400  0.50160940  0.75393459  1
  C  C46  1  0.37534817  0.12294326  0.36906195  1
  C  C47  1  0.37928118  0.13041920  0.86958079  1
  C  C48  1  0.36111897  0.62805202  0.37194794  1
  C  C49  1  0.37534817  0.63093801  0.87705673  1
  C  C50  1  0.87764427  0.12341567  0.37266968  1
  C  C51  1  0.87883343  0.12690288  0.87309711  1
  C  C52  1  0.87278066  0.62386126  0.37613870  1
  C  C53  1  0.87764427  0.62733029  0.87658433  1
  C  C54  1  0.25310400  0.25310400  -0.00413109  1
  C  C55  1  0.24889183  0.24889183  0.48414411  1
  C  C56  1  0.24966526  0.75358689  0.00068804  1
  C  C57  1  0.24606539  0.75403400  0.49839060  1
  C  C58  1  0.75358689  0.24966526  0.00068804  1
  C  C59  1  0.75403400  0.24606539  0.49839060  1
  C  C60  1  0.75006920  0.75006920  0.00192854  1
  C  C61  1  0.74654594  0.74654594  0.50232651  1
  Si  Si62  1  0.43846294  0.43846294  0.56153706  1

UKS.py