[Refactor] Separate Round logic into its own file (#570)

* Everything works, need to clean up

* cleanup

* fix rebase issue

* clang format

* docs

* clang format

* clang format

* address part of review

* Protect against edge case when discarding at end of hand

* Protect undiscard against popping a discarded card that doesn't exist

* Protect against out of bounds access to the `played` cards stack

* fix condition in `select_four_of_a_kind_cards_in_played_hand`

* change `get_played_top() + 1` to `get_played_size()`

* move `can_play/discard_hand` functions to round.c

---------

Co-authored-by: MathisMartin31 <mathis.martin31@gmail.com>

include/game/common_ui.h

@@ -24,6 +24,8 @@ enum BackgroundId
     BG_MAIN_MENU
 };
 
+enum BackgroundId get_current_background(void);
+
 /**
  * Change the background
  *