Fix missing OStream#closed? method

[RobinDaugherty]

Currently with Ruby 3.4.1 and bundler 2.6.2, when requireing a Rails application, I get the following error:

require 'path_to_application/config/application'

NoMethodError: undefined method 'closed?' for an instance of IRuby::OStream
[/opt/rbenv/versions/3.4.1/lib/ruby/3.4.0/bundler/ui/shell.rb:145](http://localhost:8888/opt/rbenv/versions/3.4.1/lib/ruby/3.4.0/bundler/ui/shell.rb#line=144):in 'Bundler::UI::Shell#tell_err'
[/opt/rbenv/versions/3.4.1/lib/ruby/3.4.0/bundler/ui/shell.rb:49](http://localhost:8888/opt/rbenv/versions/3.4.1/lib/ruby/3.4.0/bundler/ui/shell.rb#line=48):in 'Bundler::UI::Shell#error'
[/opt/rbenv/versions/3.4.1/lib/ruby/3.4.0/bundler/setup.rb:18](http://localhost:8888/opt/rbenv/versions/3.4.1/lib/ruby/3.4.0/bundler/setup.rb#line=17):in '<top (required)>'

Bundler is calling closed? on stderr https://github.com/rubygems/rubygems/blob/v3.6.2/bundler/lib/bundler/ui/shell.rb#L145

stderr is an instance of IRuby::OStream

Ruby's IO implements the closed? method: https://docs.ruby-lang.org/en/master/IO.html#method-i-closed-3F

The fix for this is to implement the closed? method. With this implementation in place, Bundler is able to run its setup.

[sealocal]

Looks good to me! Thanks for providing references. It appears this only happens when Bundler is trying to report an error, so it was difficult to repro. Thanks for solving it as a number of others have run into the issue.

[sealocal]

fixes #349