- supports schedule operation
- file_read example with liburing

- (timed_)schedule_operation ok
- file_read_operation ok

- file access generic handling
- fix dangling references to io_vec
- catching uring errors (thrown in io_service corouting)

- required kernel version 5.4 (5.5 for connect/accept operations)

- moved stdcoro.hpp into detail sub-folder

- fix: `for co_await` removed from C++20
- fix: uring operation with offset handling
- impl: `cppcoro::net::socket_disconnect_operation_impl`
- fix: naming collusion with `socket`
- fix: `GENERIC_WRITE` definition for write_only_file

- fix: io_service cancellation
- fix: increased max_events in `io_service_fixture`

- remaining deadlock in io_service_tests: multiple I/O threads servicing events
- ERROR_MORE_DATA emulation using MSG_TRUNC

- mutext protection of sge and cqe