The std.event.Loop epoll backend is now runtime-validated, not just
lower-verified: a static aarch64-linux build of the 1632-equivalent Loop test
(plus the eventfd wake path) runs 6/6 green inside an Apple `container` Linux VM
(kernel 6.18 aarch64) — add_read, idle-timeout, readable+fd+udata, the MOD-mask
add_write path, the eventfd wake channel, and EPOLLRDHUP/HUP eof all behave
identically to kqueue (lone difference: nbytes is 0 on epoll). Update the
event.sx VALIDATION note (with the re-run recipe) and the fibers checkpoint;
the epoll deliverable is complete.
e52b6c9eae