Auto merge of #95469 - ChrisDenton:unsound-read-write, r=joshtriplett

Auto merge of #95469 - ChrisDenton:unsound-read-write, r=joshtriplett

Fix unsound `File` methods

This is a draft attempt to fix #81357. *EDIT*: this PR now tackles `read()`, `write()`, `read_at()`, `write_at()` and `read_buf`. Still needs more testing though.

cc `@jstarks,` can you confirm the the Windows team is ok with the Rust stdlib using `NtReadFile` and `NtWriteFile`?

~Also, I'm provisionally using `CancelIo` in a last ditch attempt to recover but I'm not sure that this is actually a good idea. Especially as getting into this state would be a programmer error so aborting the process is justified in any case.~ *EDIT*: removed, see comments.