SWIM unit tests contain a special library for emulating the event
loop: swim_test_ev. It provides API similar to libev, but
implemented entirely in user-space, including clock functions.

The latter is the most important point, as the original libev
does not allow to define your own timing functions - internally it
relies on select/kqueue/epoll/poll/select/... with true clock.

Because of that it is impossible to perform long tests with the
original libev, which could last for minutes or even tens of
seconds if their count is big. swim_test_ev uses virtual time,
where hours can be played in milliseconds.

The fake libev is going to be re-used for Raft unit tests. But for
that it is necessary to detach it from all SWIM dependencies.

--

This commit makes all swim_test_ev functions have 'fakeev' prefix
instead of 'swim'. The functions, implementing swim_ev.h API, are
kept as one-line proxies to the fakeev functions.

Part of #5303