Have MIRV damage asymptote to 5% of total population (#1570)

## Description:

Decreasing MIRV warhead blast radius nerfed them too much, so have them
destroy 95% of population.

## 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
- [x] I have read and accepted the CLA aggreement (only required once).

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

evan

src/core/configuration/DefaultConfig.ts

@@ -23,6 +23,7 @@ import { TileRef } from "../game/GameMap";
 import { PlayerView } from "../game/GameView";
 import { UserSettings } from "../game/UserSettings";
 import { GameConfig, GameID, TeamCountConfig } from "../Schemas";
+import { NukeType } from "../StatsSchemas";
 import { assertNever, simpleHash, within } from "../Util";
 import { Config, GameEnv, NukeMagnitude, ServerConfig, Theme } from "./Config";
 import { PastelTheme } from "./PastelTheme";
@@ -822,8 +823,21 @@ export class DefaultConfig implements Config {
   }
 
   // Humans can be population, soldiers attacking, soldiers in boat etc.
-  nukeDeathFactor(humans: number, tilesOwned: number): number {
-    return (5 * humans) / Math.max(1, tilesOwned);
+  nukeDeathFactor(
+    nukeType: NukeType,
+    humans: number,
+    tilesOwned: number,
+    maxPop: number,
+  ): number {
+    if (nukeType !== UnitType.MIRVWarhead) {
+      return (5 * humans) / Math.max(1, tilesOwned);
+    }
+
+    const targetPop = 0.05 * maxPop;
+    const excessPop = Math.max(0, humans - targetPop);
+    const scalingFactor = 20000;
+
+    return (scalingFactor * excessPop * excessPop) / (maxPop * maxPop);
   }
 
   structureMinDist(): number {