Enable the @typescript-eslint/no-unused-vars eslint rule (#2130)

## Description:

### ✅ Summary of Changes

This PR enables the ESLint rule **`@typescript-eslint/no-unused-vars`**
as requested in the issue and applies the necessary code adjustments
across the project.

#### 🔧 What was done:
- Activated the rule `@typescript-eslint/no-unused-vars` in the ESLint
config.
- Updated ~70 files to comply with the rule:
  - Replaced unused variables with a `_` prefix where appropriate.
- Added inline ESLint disable comments (`eslint-disable-next-line`) for
specific cases where the variable or code block seemed important for
context, readability, or future use.
- Ensured no linting errors remain related to this rule.

---

### ❓ Clarification

Some cases were handled with inline disable comments instead of removing
the variable entirely, to avoid accidental breaking changes or loss of
intent.
If a different approach is preferred (e.g., stricter removal or
alternative handling), I’m happy to adjust the implementation
accordingly — just let me know!

---

### 🙌 Next Steps

Please review and let me know if:
- Any file should be handled differently.
- You prefer removal instead of disabling in certain areas.
- Additional rules should be enforced or reverted.

I’m available to make any follow-up improvements needed.

---

### 🎃 Hacktoberfest Note

I'm participating in **Hacktoberfest**, so if this PR is accepted,
please add the label:

`hacktoberfest-accepted`

Thank you!

#1784 

## 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:

DISCORD_USERNAME

tests/ShellRandom.test.ts

@@ -85,7 +85,6 @@ describe("Shell Random Damage", () => {
       expect(damage).toBeLessThanOrEqual(maxExpectedDamage);
     });
 
-    const uniqueDamages = new Set(damages);
     expect(damages.length).toBeGreaterThan(0);
   });
 
@@ -231,16 +230,6 @@ describe("Shell Random Damage", () => {
 
     expect(damages.length).toBeGreaterThan(0);
 
-    const baseDamage = game.config().unitInfo(UnitType.Shell).damage ?? 250;
-    const expectedDamages = [
-      Math.round((baseDamage / 250) * 200),
-      Math.round((baseDamage / 250) * 225),
-      Math.round((baseDamage / 250) * 250),
-      Math.round((baseDamage / 250) * 275),
-      Math.round((baseDamage / 250) * 300),
-      Math.round((baseDamage / 250) * 325),
-    ];
-
     const uniqueDamages = new Set(damages);
     expect(uniqueDamages.size).toBeGreaterThan(0);
 
@@ -265,7 +254,6 @@ describe("Shell Random Damage", () => {
     );
     const initialHealth = target.health();
 
-    const seed = 12345;
     const shell1 = new ShellExecution(
       game.ref(coastX, 10),
       player1,