Refactor charge generation models to avoid code duplication

    init_ver_position = np.arange(0.0, geo.row, 1.0) * geo.pixel_vert_size
    init_hor_position = np.arange(0.0, geo.col, 1.0) * geo.pixel_horz_size
    init_ver_position = np.repeat(init_ver_position, geo.col)
    init_hor_position = np.tile(init_hor_position, geo.row)
    
    init_ver_position += np.random.rand(geo.row) * geo.pixel_vert_size
    init_hor_position += np.random.rand(geo.col) * geo.pixel_horz_size

• Random position list generation should be a method of Geometry or Charge class.
• Charge generation models using this method should be reviewed, updated and standardized