Start 4.2 development

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QHHu1wodDoUBPi2Cs7yhCn

Author: claude

Gemfile.lock

@@ -22,7 +22,7 @@ GIT
 PATH
   remote: .
   specs:
-    rbs (4.1.2)
+    rbs (4.2.0.dev)
       logger
       prism (>= 1.6.0)
       tsort

lib/rbs/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module RBS
-  VERSION = "4.1.2"
+  VERSION = "4.2.0.dev"
 end