Add a Python test for checking the OFFSET is output correctly

[geographika]

@thisIsShubhamSharma - I added a Python test to create a style with doubles as OFFSET values, convert it to a string, load it back and check the doubles are still there. The test however appears to be failing. Can you convert to string and see that double OFFSET values are preserved?

          output_string = new_style.convertToString()
          new_style2 = mapscript.fromstring(output_string)
      
          # ensure attributes are output as doubles
          assert new_style.size == 7.25
  >       assert new_style2.offsetx == 10.5
  E       AssertionError: assert 0.0 == 10.5
  E        +  where 0.0 = <mapscript.mapscript.styleObj; proxy of <Swig Object of type 'styleObj *' at 0x03ED0A10> >.offsetx

[geographika]

For reference issue was #5310 and fix was by @sdlime with #5738