Enable ESLint rule no-case-declarations (#2113)

## Description:

This PR enables the ESLint rule `no-case-declarations`.
Fixes #1791 

The issue was already assigned, but since there hasn’t been any activity
for about a month, I decided to open this PR.

## 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

src/client/graphics/layers/UILayer.ts

@@ -312,7 +312,7 @@ export class UILayer implements Layer {
       return 1;
     }
     switch (unit.type()) {
-      case UnitType.Construction:
+      case UnitType.Construction: {
         const constructionType = unit.constructionType();
         if (constructionType === undefined) {
           return 1;
@@ -326,7 +326,7 @@ export class UILayer implements Layer {
           (this.game.ticks() - unit.createdAt()) /
           (constDuration === 0 ? 1 : constDuration)
         );
-
+      }
       case UnitType.MissileSilo:
       case UnitType.SAMLauncher:
         return unit.missileReadinesss();