So far, when Zeek didn't see a connection's regular tear-down (e.g.,
because its state timed-out before we got to the end), we'd still
signal a regular end-of-data to Spicy parsers. As a result, they would
then typically raise a parse error because they were probably still
expecting data and would now declare it missing. That's not very
useful because semantically it's not really a protocol issue if the
data just doesn't make it over to us; it's a transport-layer issue
that Zeek already handles elsewhere. So we now switch to signaling
end-of-data to Spicy analyzers only if the connection indeed shuts
down regularly. This is also matches how BinPAC handles it.
This also comes with a test exercising various combinations of
end-of-data behavior so that we ensure consistent/desired behavior.
Closes#4007.
