Eslint (#998)

## Description:

Enable a few eslint rules:
- `@typescript-eslint/no-empty-object-type`
- `@typescript-eslint/no-require-imports`
- `no-useless-escape`

## 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 understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

---------

Co-authored-by: Scott Anderson <scottanderson@users.noreply.github.com>

src/core/game/Game.ts

@@ -194,11 +194,11 @@ export interface UnitParamsMap {
     patrolTile: TileRef;
   };
 
-  [UnitType.Shell]: {};
+  [UnitType.Shell]: Record<string, never>;
 
-  [UnitType.SAMMissile]: {};
+  [UnitType.SAMMissile]: Record<string, never>;
 
-  [UnitType.Port]: {};
+  [UnitType.Port]: Record<string, never>;
 
   [UnitType.AtomBomb]: {
     targetTile?: number;
@@ -219,25 +219,23 @@ export interface UnitParamsMap {
     loaded?: boolean;
   };
 
-  [UnitType.Factory]: {};
+  [UnitType.Factory]: Record<string, never>;
 
-  [UnitType.MissileSilo]: {
-    cooldownDuration?: number;
-  };
+  [UnitType.MissileSilo]: Record<string, never>;
 
-  [UnitType.DefensePost]: {};
+  [UnitType.DefensePost]: Record<string, never>;
 
-  [UnitType.SAMLauncher]: {};
+  [UnitType.SAMLauncher]: Record<string, never>;
 
-  [UnitType.City]: {};
+  [UnitType.City]: Record<string, never>;
 
-  [UnitType.MIRV]: {};
+  [UnitType.MIRV]: Record<string, never>;
 
   [UnitType.MIRVWarhead]: {
     targetTile?: number;
   };
 
-  [UnitType.Construction]: {};
+  [UnitType.Construction]: Record<string, never>;
 }
 
 // Type helper to get params type for a specific unit type
@@ -381,7 +379,12 @@ export class PlayerInfo {
 }
 
 export function isUnit(unit: Unit | UnitParams<UnitType>): unit is Unit {
-  return "isUnit" in unit && typeof unit.isUnit === "function" && unit.isUnit();
+  return (
+    unit !== undefined &&
+    "isUnit" in unit &&
+    typeof unit.isUnit === "function" &&
+    unit.isUnit()
+  );
 }
 
 export interface Unit {