Ruby Head compatibility

I'm actively experimenting with the head Ruby builds (mostly due to #555) and collecting some compatibility
issues compared to 3.3 release here.

Gem/lib versions:

• ruby_wasm: 2.7.0
• js: 2.7.0

• Tempfile vs. /dev/null: https://github.com/ruby/tempfile/pull/38

This commit broke loading tempfile.rb: https://github.com/ruby/ruby/commit/136cbf04419acf993357701e54712f921a294355

require "tempfile"

# => 'File#initialize': No such file or directory @ rb_sysopen - /dev/null (Errno::ENOENT)

Not sure how to properly handle /dev/null in Wasm, though; maybe, we should return nil for IO::NULL and check for nil-ness whenever it's used 🤔

• Fails to require digest/sha1: https://github.com/ruby/digest/pull/71

require "digest/sha1"

#=> <internal:/usr/local/lib/ruby/3.4.0+0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require': rb_digest_wrap_metadata not found (LoadError)
<internal:/usr/local/lib/ruby/3.4.0+0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
eval:3:in '<main>'
-e:in 'Kernel.eval'

Worked fine in 3.3.

Reproduce the two failures with ruby.wasm 2.7.0, starting with the require examples for tempfile.rb and digest/sha1. Review the referenced tempfile and digest pull requests and the Ruby commit, then compare behavior with Ruby 3.3. Done means both libraries load successfully in the head WebAssembly build.