Make `From` impls of NonZero integer const. I also changed the feature gate added to `From` impls of Atomic integer to `const_num_from_num` from `const_convert`. Tracking issue: #87852
Make `From` impls of NonZero integer const. I also changed the feature gate added to `From` impls of Atomic integer to `const_num_from_num` from `const_convert`. Tracking issue: #87852