Consider implementing eof

[sk-]

Currently down only implements eof?, but in io streams eof? Is an alias for eof, as seen in the docs https://docs.ruby-lang.org/en/master/IO.html#method-i-eof

The issue we are having with the lack of the eof method is that ruby zip fails in this line https://github.com/rubyzip/rubyzip/blob/1f3f84c88914b2b3c77c18b73f2ecb42225a54af/lib/zip/crypto/decrypted_io.rb#L35