Enable the @typescript-eslint/prefer-readonly eslint rule (#1859)

## Description:

Enable the `@typescript-eslint/prefer-readonly` eslint rule.

## 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

src/core/execution/NukeExecution.ts

@@ -24,9 +24,9 @@ export class NukeExecution implements Execution {
   private pathFinder: ParabolaPathFinder;
 
   constructor(
-    private nukeType: NukeType,
-    private player: Player,
-    private dst: TileRef,
+    private readonly nukeType: NukeType,
+    private readonly player: Player,
+    private readonly dst: TileRef,
     private src?: TileRef | null,
     private speed = -1,
     private waitTicks = 0,