Enable strictNullChecks, eqeqeq (#436)

## Description:

Improve type safety and runtime correctness by:
1. Enabling TypeScript's
[strictNullChecks](https://www.typescriptlang.org/tsconfig/#strictNullChecks)
compiler option.
2. Replacing all loose equality operators (`==` and `!=`) with strict
equality operators (`===` and `!==`).
3. Cleaning up of type declarations, null handling logic, and equality
expressions throughout the project.

Currently, the code allows implicit assumptions that `null` and
`undefined` are interchangeable, and relies on type-coercing equality
checks that can introduce subtle bugs. These practices make it difficult
to reason about when values may be absent and hinder the effectiveness
of static analysis.

Migrating to strict null checks and enforcing strict equality
comparisons will clarify intent, reduce bugs, and make the codebase
safer and easier to maintain.

Fixes #466 

## 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

---------

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

src/client/LocalServer.ts

@@ -26,7 +26,7 @@ export class LocalServer {
 
   private paused = false;
 
-  private winner: ClientSendWinnerMessage = null;
+  private winner: ClientSendWinnerMessage | null = null;
   private allPlayersStats: AllPlayersStats = {};
 
   private turnsExecuted = 0;
@@ -43,7 +43,7 @@ export class LocalServer {
 
   start() {
     this.turnCheckInterval = setInterval(() => {
-      if (this.turnsExecuted == this.turns.length) {
+      if (this.turnsExecuted === this.turns.length) {
         if (
           this.isReplay ||
           Date.now() >
@@ -62,6 +62,9 @@ export class LocalServer {
         this.lobbyConfig.gameRecord,
       ).turns;
     }
+    if (this.lobbyConfig.gameStartInfo === undefined) {
+      throw new Error("missing gameStartInfo");
+    }
     this.clientMessage(
       ServerStartGameMessageSchema.parse({
         type: "start",
@@ -84,13 +87,13 @@ export class LocalServer {
     const clientMsg: ClientMessage = ClientMessageSchema.parse(
       JSON.parse(message),
     );
-    if (clientMsg.type == "intent") {
+    if (clientMsg.type === "intent") {
       if (this.lobbyConfig.gameRecord) {
         // If we are replaying a game, we don't want to process intents
         return;
       }
       if (this.paused) {
-        if (clientMsg.intent.type == "troop_ratio") {
+        if (clientMsg.intent.type === "troop_ratio") {
           // Store troop change events because otherwise they are
           // not registered when game is paused.
           this.intents.push(clientMsg.intent);
@@ -99,7 +102,7 @@ export class LocalServer {
       }
       this.intents.push(clientMsg.intent);
     }
-    if (clientMsg.type == "hash") {
+    if (clientMsg.type === "hash") {
       if (!this.lobbyConfig.gameRecord) {
         // If we are playing a singleplayer then store hash.
         this.turns[clientMsg.turnNumber].hash = clientMsg.hash;
@@ -113,7 +116,7 @@ export class LocalServer {
         );
         return;
       }
-      if (archivedHash != clientMsg.hash) {
+      if (archivedHash !== clientMsg.hash) {
         console.error(
           `desync detected on turn ${clientMsg.turnNumber}, client hash: ${clientMsg.hash}, server hash: ${archivedHash}`,
         );
@@ -131,7 +134,7 @@ export class LocalServer {
         );
       }
     }
-    if (clientMsg.type == "winner") {
+    if (clientMsg.type === "winner") {
       this.winner = clientMsg;
       this.allPlayersStats = clientMsg.allPlayersStats;
     }
@@ -172,6 +175,9 @@ export class LocalServer {
         clientID: this.lobbyConfig.clientID,
       },
     ];
+    if (this.lobbyConfig.gameStartInfo === undefined) {
+      throw new Error("missing gameStartInfo");
+    }
     const record = createGameRecord(
       this.lobbyConfig.gameStartInfo.gameID,
       this.lobbyConfig.gameStartInfo,
@@ -179,8 +185,8 @@ export class LocalServer {
       this.turns,
       this.startedAt,
       Date.now(),
-      this.winner?.winner,
-      this.winner?.winnerType,
+      this.winner?.winner ?? null,
+      this.winner?.winnerType ?? null,
       this.allPlayersStats,
     );
     if (!saveFullGame) {