anim_to_vtk: yz and zx stress components swapped in VTK tensor output (solid & SPH)

[pxiaohui2022-crypto]

Bug

In output_converters/anim_to_vtk/src/anim_to_vtk.cpp, the 3×3 tensor
matrix written to the legacy VTK TENSORS block places the yz and zx
components in the wrong off-diagonal positions.

The 6 tensor values read from the anim file are ordered xx,yy,zz,xy,yz,zx
(indices 0..5), as the comment at line 576 correctly states.

A symmetric tensor must be written as:

| xx  xy  zx |   indices  | 0  3  5 |
| xy  yy  yz |     -->    | 3  1  4 |
| zx  yz  zz |            | 5  4  2 |

But the current code writes index 4 (yz) at position (1,3)/(3,1) and
index 5 (zx) at position (2,3)/(3,2) — they are swapped.

Affected lines

• Solid elements — anim_to_vtk.cpp:1473-1475
• SPH elements — anim_to_vtk.cpp:1575-1577 (identical bug)

The 2D shell block (lines 1366-1369) is correct (only 3 components).

Ground truth

The component order is confirmed by the engine's stress-rotation routine
engine/source/output/anim/generate/srota6.F:200-205:

L11=TENS(1) L22=TENS(2) L33=TENS(3)  -> xx yy zz
L12=TENS(4) L23=TENS(5) L13=TENS(6)  -> xy yz zx

tensor6.F writes TENS(1..6) verbatim into the anim file, so index 4 is
yz and index 5 is zx (= xz).

Suggested fix

In both blocks, swap offsets + 4 and + 5 so the matrix becomes:

// row 1: idx 0, 3, 5
// row 2: idx 3, 1, 4
// row 3: idx 5, 4, 2