Auto merge of #75005 - adamreichold:limit-vector-count, r=Amanieu
Auto merge of #75005 - adamreichold:limit-vector-count, r=Amanieu

Limit I/O vector count on Unix

Unix systems enforce limits on the vector count when performing vectored I/O via the readv and writev system calls and return EINVAL when these limits are exceeded. This changes the standard library to handle those limits as short reads and writes to avoid forcing its users to query these limits using platform specific mechanisms.

Fixes #68042

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