freeFields method
Frees internal fields (like strings) that were allocated on the C heap. Does NOT free the struct itself.
nativeFree must be the free function matching the allocator that
produced the fields — for native-returned structs, the module's
_nitroFree (the exported C-runtime free). package:ffi's malloc.free
is CoTaskMemFree on Windows and corrupts the heap on these pointers.
Implementation
void freeFields(void Function(Pointer<NativeType>) nativeFree) {}