Set a targetable status for nukes (#1174)

## Description:

Set a targetable status for units (specifically atom bomb and hydro)
A nuke is targetable near launch and target but is untargetable mid air.
An untargetable unit is half transparent to show that it cannot be
destroyed.


![targetable](https://github.com/user-attachments/assets/cc6769ff-95ab-4294-9a8e-10f909711f68)

## 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

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

Vivacious Box

src/client/graphics/layers/UnitLayer.ts

@@ -535,6 +535,11 @@ export class UnitLayer implements Layer {
     );
 
     if (unit.isActive()) {
+      const targetable = unit.targetable();
+      if (!targetable) {
+        this.context.save();
+        this.context.globalAlpha = 0.4;
+      }
       this.context.drawImage(
         sprite,
         Math.round(x - sprite.width / 2),
@@ -542,6 +547,9 @@ export class UnitLayer implements Layer {
         sprite.width,
         sprite.width,
       );
+      if (!targetable) {
+        this.context.restore();
+      }
     }
   }
 }