Clean up and refactor the Unit class (#769)

## Description:

* Merged similar fields so they can be reused (eg warshipTarget =>
targetUnit)
* simplified isCooldown api
* added "touch" method to send update to UI layer
* standardized on "undefined"


## Please complete the following:

- [ ] I have added screenshots for all UI updates
- [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:

<DISCORD USERNAME>
evan

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **Refactor**
- Unified and simplified how unit targets and cooldowns are managed
across all unit types, resulting in more consistent in-game behavior for
nukes, warships, trade ships, and SAM launchers.
- Updated naming and logic for unit targeting and cooldowns, improving
clarity in status displays and interactions.
- Reorganized unit interface and streamlined cooldown handling for
smoother gameplay experience.
- **Bug Fixes**
- Corrected visual indicators for nukes and warships to accurately
reflect their targets.
- **Tests**
- Updated automated tests to align with the new cooldown and targeting
logic.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/core/game/GameView.ts

@@ -8,7 +8,6 @@ import {
   GameUpdates,
   Gold,
   NameViewData,
-  nukeTypes,
   Player,
   PlayerActions,
   PlayerBorderTiles,
@@ -83,7 +82,7 @@ export class UnitView {
     return this.data.pos;
   }
   owner(): PlayerView {
-    return this.gameView.playerBySmallID(this.data.ownerID) as PlayerView;
+    return this.gameView.playerBySmallID(this.data.ownerID)! as PlayerView;
   }
   isActive(): boolean {
     return this.data.isActive;
@@ -97,20 +96,11 @@ export class UnitView {
   constructionType(): UnitType | undefined {
     return this.data.constructionType;
   }
-  dstPortId(): number | undefined {
-    return this.data.dstPortId;
+  targetUnitId(): number | undefined {
+    return this.data.targetUnitId;
   }
-  detonationDst(): TileRef | undefined {
-    if (!nukeTypes.includes(this.type())) {
-      throw Error("Must be a nuke");
-    }
-    return this.data.detonationDst;
-  }
-  warshipTargetId(): number | undefined {
-    if (this.type() !== UnitType.Warship) {
-      throw Error("Must be a warship");
-    }
-    return this.data.warshipTargetId;
+  targetTile(): TileRef | undefined {
+    return this.data.targetTile;
   }
   ticksLeftInCooldown(): Tick | undefined {
     return this.data.ticksLeftInCooldown;