Replace Timeout.timeout with TCPSocket.open(open_timeout:) when available

[osyoyu]

Resolves #6.

This patch replaces the implementation of #open_timeout from Timeout.timeout from the builtin timeout in TCPSocket.open, which was introduced in Ruby 3.5 (https://bugs.ruby-lang.org/issues/21347).

The builtin timeout in TCPSocket.open is better in several ways. First, it does not rely on a separate Ruby Thread for monitoring Timeout (which is what the timeout library internally does). Also, it is compatible with Ractors, since it does not rely on Mutexes (which is also what the timeout library does).

This change allows the following code to work.

require 'net/http'
Ractor.new {
  uri = URI('http://example.com/')
  http = Net::HTTP.new(uri.host, uri.port)
  http.open_timeout = 1
  http.get(uri.path)
}.value

In Ruby <3.5 environments where TCPSocket.open does not have the open_timeout option, I have kept the behavior unchanged. net/http will use Timeout.timeout { TCPSocket.open }.

Changes in behavior

On timeout, the raised Net::OpenTimeout's message has slightly changed, and also carrys a Errno::ETIMEDOUT as its cause.

/home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1670:in 'Net::HTTP#connect': Failed to open TCP connection to example.com:80 (Connection timed out - user specified timeout) (Net::OpenTimeout)
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1636:in 'Net::HTTP#do_start'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1625:in 'Net::HTTP#start'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:2378:in 'Net::HTTP#request'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1993:in 'Net::HTTP#get'
	from nethttptest.rb:13:in '<main>'
/home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1660:in 'TCPSocket#initialize': Connection timed out - user specified timeout (Errno::ETIMEDOUT)
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1660:in 'IO.open'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1660:in 'Net::HTTP#connect'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1636:in 'Net::HTTP#do_start'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1625:in 'Net::HTTP#start'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:2378:in 'Net::HTTP#request'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1993:in 'Net::HTTP#get'
	from nethttptest.rb:13:in '<main>'

Previously, it looked like this.

/home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1665:in 'TCPSocket#initialize': Failed to open TCP connection to example.com:80 (execution expired) (Net::OpenTimeout)
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1665:in 'IO.open'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1665:in 'block in Net::HTTP#connect'
	from /home/osyoyu/.rbenv/versions/3.4.5/lib/ruby/3.4.0/timeout.rb:185:in 'block in Timeout.timeout'
	from /home/osyoyu/.rbenv/versions/3.4.5/lib/ruby/3.4.0/timeout.rb:192:in 'Timeout.timeout'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1664:in 'Net::HTTP#connect'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1636:in 'Net::HTTP#do_start'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1625:in 'Net::HTTP#start'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:2378:in 'Net::HTTP#request'
	from /home/osyoyu/Development/rubyorg/net-http/lib/net/http.rb:1993:in 'Net::HTTP#get'
	from nethttptest.rb:13:in '<main>'

[osyoyu]

This version needs ruby/ruby#13909. It's now merged!

[osyoyu]

I couldn't come up with a better way to detect the absence of open_timeout: option. Is this a acceptable solution?

TCPSocket.open is basically (**args) from the perspective of Ruby, so Method#parameters wasn't an option:

irb(main):001> require 'socket'
=> true
irb(main):002> TCPSocket.method(:open).parameters
=> [[:rest]]