rust/vmstate: Add unit test for vmstate_{of|struct} macro

rust/vmstate: Add unit test for vmstate_{of|struct} macro

Add a unit test to cover some patterns accepted by vmstate_of and
vmstate_struct macros, which correspond to the following C version
macros:

 * VMSTATE_BOOL_V
 * VMSTATE_U64
 * VMSTATE_STRUCT_VARRAY_UINT8
 * (no C version) MULTIPLY variant of VMSTATE_STRUCT_VARRAY_UINT32
 * VMSTATE_ARRAY

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250318130219.1799170-13-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>