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. 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 }`.

Author: osyoyu

lib/net/http.rb

@@ -1654,14 +1654,22 @@ 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?