Add eslint and fix eslint errors, other minor improvements

eslint.config.mjs

@@ -0,0 +1,47 @@
+import eslint from "@eslint/js";
+import tseslint from "typescript-eslint";
+import stylistic from "@stylistic/eslint-plugin";
+
+export default tseslint.config({
+	extends: [
+		eslint.configs.recommended,
+		tseslint.configs.recommendedTypeChecked,
+	],
+	files: ["packages/*/src/**/*.{ts,tsx}"],
+	plugins: {
+		"@stylistic": stylistic,
+	},
+	languageOptions: {
+		parserOptions: {
+			projectService: true,
+			tsconfigRootDir: import.meta.dirname,
+		},
+	},
+	rules: {
+		"@stylistic/comma-dangle": ["error", "always-multiline"],
+		"@stylistic/member-delimiter-style": ["error", {
+			singleline: {
+				delimiter: "comma",
+				requireLast: false,
+			},
+			multiline: {
+				delimiter: "comma",
+				requireLast: true,
+			},
+			overrides: {
+				interface: {
+					singleline: {
+						delimiter: "semi",
+					},
+					multiline: {
+						delimiter: "semi",
+					},
+				},
+			},
+		}],
+		"@stylistic/semi": ["error", "always"],
+		"@typescript-eslint/no-explicit-any": "off",
+		"@typescript-eslint/no-namespace": "off",
+		"@typescript-eslint/no-misused-promises": ["error", { checksVoidReturn: false }],
+	},
+});