Add setup scripts for development: bin/setup (bash and bat)

- Added bin/setup (bash) and bin/setup.bat (Windows) for development environment setup.
- Both scripts install dependencies via Bundler and build stub executables required for testing.
- Bash version is kept minimal for terminal-savvy developers.
- Windows version uses echo prompts for better visibility.

Author: shinokaro

bin/setup

@@ -4,3 +4,4 @@ IFS=$'\n\t'
 set -vx
 
 bundle install
+bundle exec rake build_stub

bin/setup.bat

@@ -17,6 +17,14 @@ if errorlevel 1 (
   exit /b 1
 )
 
+echo == Building stub executables ==
+
+call bundle exec rake build_stub
+if errorlevel 1 (
+  echo Failed to build stubs.
+  exit /b 1
+)
+
 echo == Setup completed ==
 
 endlocal