input: Write a function named "Transpile" that takes four arguments: "src_dir", "dst_dir", "model_filename", and "params_filename". The function should create a CPUPlace and an Executor using Paddle Fluid, and a Scope object. It should load an inference program and its associated targets using `fluid.io.load_inference_model` with the provided arguments, clone the inference program, and apply the inference transpiler. The optimized inference program should be saved to the specified destination directory. If the destination directory does not exist, it should be created. Finally, create a main function that uses argparse to parse command-line arguments and calls the "Transpile" function with the parsed arguments.
  
  assert call_transpile("./src_dir", "./dst_dir", "model.pdmodel", "model.pdiparams") == None
  assert call_transpile("./invalid_src_dir", "./dst_dir", "model.pdmodel", "model.pdiparams") == None
  assert call_transpile("./src_dir", "./non_existent_dst_dir", "model.pdmodel", "model.pdiparams") == None
  assert call_transpile("./src_dir", "./dst_dir", "non_existent_model.pdmodel", "model.pdiparams") == None
  
  where `call_transpile` is a helper function that simulates the call to `Transpile` function in the given specification.
output: 
  import os
  import paddle.fluid as fluid
  
  def Transpile(src_dir, dst_dir, model_filename, params_filename):
      place = fluid.CPUPlace()
      exe = fluid.Executor(place)
      scope = fluid.core.Scope()
      
      if not os.path.exists(dst_dir):
          os.makedirs(dst_dir)
      
      [inference_program, feed_target_names, fetch_targets] = fluid.io.load_inference_model(
          dirname=src_dir,
          executor=exe,
          model_filename=model_filename,
          params_filename=params_filename
      )
      
      transpiled_program = fluid.compiler.CompiledProgram(inference_program).with_data_parallel()
      
      fluid.io.save_inference_model(
          dirname=dst_dir,
          feeded_var_names=feed_target_names,
          target_vars=fetch_targets,
          executor=exe,
          main_program=transpiled_program.program
      )
  