Migrate Backend to Strict TypeScript

eslint.config.js

@@ -0,0 +1,54 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+export default tseslint.config(
+  {
+    ignores: [
+      "node_modules/**",
+      "dist/**", 
+      "build/**",
+      "**/*.js",
+      "**/dist/**",
+      "launchdarkly/**/dist/**"
+    ]
+  },
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    languageOptions: {
+      parser: tseslint.parser,
+      parserOptions: {
+        ecmaVersion: 2020,
+        sourceType: "module",
+        project: [
+          "./tsconfig.json",
+          "./launchdarkly/tsconfig.json",
+          "./launchdarkly/node/tsconfig.json",
+          "./launchdarkly/react/tsconfig.json"
+        ]
+      },
+      globals: {
+        console: "readonly",
+        process: "readonly"
+      }
+    },
+    rules: {
+      "@typescript-eslint/explicit-function-return-type": "warn",
+      "@typescript-eslint/no-explicit-any": "warn", 
+      "@typescript-eslint/prefer-nullish-coalescing": "warn",
+      "@typescript-eslint/explicit-member-accessibility": [
+        "error",
+        {
+          "accessibility": "explicit",
+          "overrides": {
+            "accessors": "explicit",
+            "constructors": "explicit",
+            "methods": "explicit",
+            "properties": "explicit",
+            "parameterProperties": "explicit"
+          }
+        }
+      ]
+    }
+  }
+);