Move the SSE parsing tests from a fixture that started a server and an
SSEClient for every case to unit tests of detail::SSEParser, and turn
NonDigitRetryFieldIgnored, which slept for 500ms, into one of them. Add
tests that feed each stream split at every position and byte by byte,
and that cover the max event length and an event left incomplete at the
end of the stream.
yhirose
a39e081386
