Auto merge of #83390 - clarfonthey:hasher_docs, r=Amanieu
Auto merge of #83390 - clarfonthey:hasher_docs, r=Amanieu

Document Hasher spec decision from #42951

Since that ticket was closed without the decision actually being documented.

Fixes #42951.

graydon/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust