The current default offset is 0 which means read/write will not
work like POSIX read/write and update the file position and instead will
always work at the beginning of the file.

Since linux v5.5 (ba04291eb66ed895f194ae5abd3748d72bf8aaea) io_uring
supports offset=-1 which behaves like pvread2/pvwrite2.
This feature is reported by IORING_FEAT_RW_CUR_POS.

By using the default offset -1 emper::io::readFile and emper::io::writeFile
will work like write/read but does also support pwrite/pread.