Unit tests for parallax_2d

[LeonStansfield]

trafficstars

In this PR I have added unit tests for parallax_2d.h for the tracker #43440 The tests include

• set_scroll_scale and get_scroll_scale
• set_repeat_size and get_repeat_size
• set_repeat_times and get_repeat_times
• set_autoscroll and get_autoscroll
• set_scroll_offset and get_scroll_offset
• set_screen_offset and get_screen_offset
• set_limit_begin and get_limit_begin
• set_limit_end and get_limit_end
• set_follow_viewport and get_follow_viewport
• set_ignore_camera_scroll and is_ignore_camera_scroll

[Calinou]

cc @markdibarry

[AThousandShips]

Please use clang-format or the precommit hook, see here, to fix your style instead

[kleonc]

Please squash commits into one, see PR workflow (and ensure the resulting commit has a short descriptive title).

[AThousandShips]

Please fix the commit message to follow the style, the PR title would be good

[akien-mga]

Thanks!