feat: remove spawn timer on singleplayer (#3199)

Resolves #1041 

## Description:

Remove the singleplayer spawn countdown so the game starts when the
player spawns, spawn nations immediately after player spawn, and align
game timer/max-timer timing with the new start point.

Added a singleplayer regression test for spawn-immunity timing
(GameImpl.test.ts) and updated spawn-phase loop tests to use gameType:
GameType.Public where singleplayer behavior is not under test (e.g.
MIRV/AI/Spawn/WinCheck-related suites), eliminating inSpawnPhase()
timeout hangs after the new singleplayer start logic.


https://github.com/user-attachments/assets/c07a585f-1153-490e-88ca-a91fc7ae5756

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:
aotumuri

tests/ShellRandom.test.ts

@@ -19,20 +19,13 @@ describe("Shell Random Damage", () => {
   beforeEach(async () => {
     game = await setup(
       "half_land_half_ocean",
-      {
-        infiniteGold: true,
-        instantBuild: true,
-      },
+      { infiniteGold: true, instantBuild: true },
       [
         new PlayerInfo("attacker", PlayerType.Human, null, "player_1_id"),
         new PlayerInfo("defender", PlayerType.Human, null, "player_2_id"),
       ],
     );
 
-    while (game.inSpawnPhase()) {
-      game.executeNextTick();
-    }
-
     player1 = game.player("player_1_id");
     player2 = game.player("player_2_id");
   });