MEM-ZERO contradicts LANG-UNSAFE

[aleksator]

In MEM-ZERO it is recommended to use unsafe function std::ptr::write_volatile(), when it does not fall under exceptions of LANG-UNSAFE.
The exceptions should probably be extended to cover the use of this function.

[hg-anssi]

This issue should be included in a more general question about reshaping / removing the zeroing example.

[hg-anssi]

reformulate with more general LANG-UNSAFE.