Refactors, fix, and features

[sgerbino]

Usurps #11.

feat: add CancelIoEx support for accept operations on Windows

• Add virtual do_cancel() hook to overlapped_op base class
• Implement accept_op::do_cancel() calling CancelIoEx on listen socket
• Wire canceller to invoke do_cancel() after request_cancel()

feat: implement cancellation for read and write socket operations

• Add do_cancel() implementation for read_op using CancelIoEx
• Add do_cancel() implementation for write_op using CancelIoEx
• Add win_socket_impl reference to read_op and write_op structs
• Initialize read and write operations with socket impl in constructor

fix: add cancellation support for Windows socket connect

• Add impl reference and do_cancel() override to connect_op struct
• Implement connect_op::do_cancel() calling CancelIoEx on the socket
• Initialize conn_ member with socket impl reference in constructor

chore: relocate sources and add build presets

• move implementation sources under src/corosio/src and adjust build files
• add CMakePresets.json default Ninja configure to out/build
• note portable capy::cond comparisons in docs and public API comments
• refresh ignore rules to keep build scripts while ignoring outputs