Make nations more forgiving toward humans on Easy difficulty 🕊️ (#3791)

## Description:

- Nations on Easy no longer betray human allies
- Nations on Easy now attack humans only 25% of the time (down from 50%)
- Increased Easy reaction tick range (65-100, up from 65-80) so nations
respond more slowly
- Raised MIRV steamroll-stop thresholds on Easy (city gap multiplier 1.5
-> 2, min leader cities 15 -> 20) and slightly tuned Medium/Hard
thresholds

## 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:

FloPinguin

src/core/execution/utils/AiAttackBehavior.ts

@@ -767,7 +767,7 @@ export class AiAttackBehavior {
 
     // Prevent attacking of humans on lower difficulties
     const { difficulty } = this.game.config().gameConfig();
-    if (difficulty === Difficulty.Easy && this.random.chance(2)) {
+    if (difficulty === Difficulty.Easy && this.random.nextInt(0, 4) !== 0) {
       return false;
     }
     if (difficulty === Difficulty.Medium && this.random.chance(4)) {