The current API does not allow the user to distinguish between EOF and
an empty line. Reader.readUntilDelimiterOrEof() gets this API right so
update readUntilDelimiterOrEofAlloc() to match it. Returning an optional
here additionally makes calling this in a loop much cleaner.

Remove readUntilDelimiterOrEofArrayList() as it no longer needed to
implement readUntilDelimiterOrEof() and has the same API issues
described without a clear way to fix them.