Fix various ESLint violations (#402)

## Description:

Fixes a number of ESLint violations. Although I have tested these
changes through the local dev server, I don't have a high confidence
that the testing is sufficient, as I am new to this codebase. This
change would benefit from heightened scrutiny.

## Please complete the following:

- [x] 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:

fake.neo

---------

Co-authored-by: Scott Anderson <662325+scottanderson@users.noreply.github.com>

src/core/game/Game.ts

@@ -137,8 +137,8 @@ export class Cell {
   private strRepr: string;
 
   constructor(
-    public readonly x,
-    public readonly y,
+    public readonly x: number,
+    public readonly y: number,
   ) {
     this.strRepr = `Cell[${this.x},${this.y}]`;
   }

src/core/game/GameImpl.ts

@@ -141,7 +141,7 @@ export class GameImpl implements Game {
   }
 
   addUpdate(update: GameUpdate) {
-    (this.updates[update.type] as any[]).push(update);
+    (this.updates[update.type] as GameUpdate[]).push(update);
   }
 
   nextUnitID(): number {
@@ -383,7 +383,7 @@ export class GameImpl implements Game {
   }
 
   playerByClientID(id: ClientID): Player | null {
-    for (const [pID, player] of this._players) {
+    for (const [, player] of this._players) {
       if (player.clientID() == id) {
         return player;
       }

src/core/game/PlayerImpl.ts

@@ -1004,7 +1004,7 @@ export class PlayerImpl implements Player {
   // It's a probability list, so if an element appears twice it's because it's
   // twice more likely to be picked later.
   tradingPorts(port: Unit): Unit[] {
-    let ports = this.mg
+    const ports = this.mg
       .players()
       .filter((p) => p != port.owner() && p.canTrade(port.owner()))
       .flatMap((p) => p.units(UnitType.Port))