Resolve linter issues, add unit tests, adjust test coverage

qr-api/eslint.config.cjs

@@ -0,0 +1,28 @@
+'use strict';
+
+const tsParser = require('@typescript-eslint/parser');
+const tsPlugin = require('@typescript-eslint/eslint-plugin');
+const prettierConfig = require('eslint-config-prettier');
+
+module.exports = [
+    { ignores: ['node_modules/', 'dist/', 'coverage/', '*.tsbuildinfo'] },
+    {
+        files: ['**/*.ts'],
+        languageOptions: {
+            ecmaVersion: 2022,
+            sourceType: 'module',
+            parser: tsParser,
+            parserOptions: { project: null },
+        },
+        plugins: { '@typescript-eslint': tsPlugin },
+        rules: {
+            ...tsPlugin.configs.recommended.rules,
+            '@typescript-eslint/no-unused-vars': [
+                'warn',
+                { argsIgnorePattern: '^_' },
+            ],
+            '@typescript-eslint/no-explicit-any': 'warn',
+        },
+    },
+    prettierConfig,
+];