Expose waitable handles in Windows

[notgull]

This commit allows waitable handles to be polled in Windows. This allows I/O constructs like processes, mutexes and waitable events be registered into the poller and be polled just like anything else.

cc #25

[notgull]

OpenBSD CI failed spuriously I think

[fogti]

poller API nitpick (although not really related to this PR): why are the poller methods for sockets and handles named wildly different?

[notgull]

Because I missed that when I was implementing that API in smol-rs/polling#111

[fogti]

looks good overall, although I'll need to find time to test this on windows...

[h33p]

I'm able to use this to integrate completion I/O with async-io memflow/mfio@088e32c

Works on wine:

❯ WINEDEBUG="-all" RUST_BACKTRACE=1 RUST_LOG="mfio_rt::test_suite=trace,mfio_rt=debug" MFIO_FS_BACKENDS=iocp wine64 ./target/x86_64-pc-windows-gnu/release/deps/mfio_rt-46d6aa56a31792b4.exe smol

running 36 tests
test native::suite_tests::smol::net_tests_all::tcp_connect ... ok
test native::suite_tests::smol::net_tests_all::tcp_listen ... ok
test native::suite_tests::smol::net_tests_default::tcp_connect ... ok
test native::suite_tests::smol::net_tests_all::tcp_send_seq ... ok
test native::suite_tests::smol::net_tests_all::tcp_send_con ... ok
test native::suite_tests::smol::net_tests_all::tcp_receive_seq ... ok
test native::suite_tests::smol::net_tests_all::tcp_receive_con ... ok
test native::suite_tests::smol::net_tests_default::tcp_listen ... ok
test native::suite_tests::smol::net_tests_all::tcp_echo_server_con ... ok
test native::suite_tests::smol::net_tests_default::tcp_echo_server_seq ... ok
test native::suite_tests::smol::net_tests_default::tcp_echo_client_con ... ok
test native::suite_tests::smol::net_tests_all::tcp_echo_server_seq ... ok
test native::suite_tests::smol::net_tests_default::tcp_receive_con ... ok
test native::suite_tests::smol::net_tests_default::tcp_echo_server_con ... ok
test native::suite_tests::smol::net_tests_default::tcp_send_con ... ok
test native::suite_tests::smol::net_tests_default::tcp_receive_seq ... ok
test native::suite_tests::smol::net_tests_default::tcp_send_seq ... ok
test native::suite_tests::smol::tests_all::dirs_equal ... ok
test native::suite_tests::smol::tests_all::files_equal ... ok
test native::suite_tests::smol::net_tests_all::tcp_echo_client_con ... ok
test native::suite_tests::smol::net_tests_default::tcp_echo_client_seq ... ok
test native::suite_tests::smol::tests_all::files_equal_rel ... ok
test native::suite_tests::smol::tests_default::dirs_equal ... ok
test native::suite_tests::smol::tests_all::writes_equal ... ok
test native::suite_tests::smol::tests_default::files_equal ... ok
test native::suite_tests::smol::tests_all::writes_equal_rel ... ok
test native::suite_tests::smol::tests_default::files_equal_rel ... ok
test native::suite_tests::smol::tests_all::walk_dirs ... ok
test native::suite_tests::smol::tests_default::writes_equal ... ok
test native::suite_tests::smol::tests_default::walk_dirs ... ok
test native::suite_tests::smol::tests_default::writes_equal_rel ... ok
test native::suite_tests::smol::net_tests_all::tcp_echo_client_seq ... ok
test native::suite_tests::smol::tests_default::all_tests_con ... ok
test native::suite_tests::smol::tests_default::all_tests_seq ... ok
test native::suite_tests::smol::tests_all::all_tests_con ... ok
test native::suite_tests::smol::tests_all::all_tests_seq ... ok

Do not have a windows native machine at hand, however.