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

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 than Timeout.timeout. It does not rely on a separate Ruby Thread for monitoring Timeout (which is what the timeout library internally does).

Furthermore, it is compatible with Ractors, as opposed to Timeout.timeout (it internally uses Thread::Mutex which can not be used in non-main Ractors).
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 }`.

Author: osyoyu

lib/net/http.rb

@@ -1672,14 +1672,22 @@ def connect
       end
 
       debug "opening connection to #{conn_addr}:#{conn_port}..."
-      s = Timeout.timeout(@open_timeout, Net::OpenTimeout) {
-        begin
-          TCPSocket.open(conn_addr, conn_port, @local_host, @local_port)
-        rescue => e
-          raise e, "Failed to open TCP connection to " +
-            "#{conn_addr}:#{conn_port} (#{e.message})"
+      begin
+        s = begin
+          # Use built-in timeout in TCPSocket.open if available
+          TCPSocket.open(conn_addr, conn_port, @local_host, @local_port, open_timeout: @open_timeout)
+        rescue ArgumentError => e
+          raise if !e.message.include?('unknown keyword: :open_timeout')
+          # Fallback to Timeout.timeout if TCPSocket.open does not support open_timeout
+          Timeout.timeout(@open_timeout, Net::OpenTimeout) {
+            TCPSocket.open(conn_addr, conn_port, @local_host, @local_port)
+          }
         end
-      }
+      rescue => e
+        e = Net::OpenTimeout.new(e) if e.is_a?(Errno::ETIMEDOUT) # for compatibility with previous versions
+        raise e, "Failed to open TCP connection to " +
+          "#{conn_addr}:#{conn_port} (#{e.message})"
+      end
       s.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
       debug "opened"
       if use_ssl?