✨ safeio Add support for cancelling readers that make blocking kernel reads during copying

[joshjennings98]

Description

Add support for cancelling readers that make blocking kernel reads during copying to safeio submodule.

When copying, a lot of the time things were in the kernel read and therefore since the cancel in the other contextual readers only cancel before a read, they weren't be cancelled.

This allows readclosers to be used and makes it so that context cancellation will call their close functions which will stop the kernel read.

https://man7.org/linux/man-pages/man2/read.2.html

Test Coverage

• This change is covered by existing or additional automated tests.
• Manual testing has been performed (and evidence provided) as automated testing was not feasible.
• Additional tests are not required for this change (e.g. documentation update).