refactor: Enable stylistic ESLint rules

* Migrate to the new "flat" eslint config [1]
    * The eslintrc format will be deprecated and removed in ESLint v10
    * ESLint plugins in your IDE might still require a "useFlatConfig"
      setting to be set until ESLint 9 is released [4]
* Migrate from @typescript-eslint/eslint-plugin to typescript-eslint [2]
* Enable TypeScript compiler to process test/ dir
    * Separate "tsconfig.build.json" is used for releases and still
      only includes sources
    * Before,  no TypeScript validation occurced in test files
* Enable and enforce "ESLint Stylistic" rules [3]
* Unfortunately I failed to get the eslint-plugin-ava working with
  TypeScript

[1]: https://eslint.org/docs/latest/use/configure/configuration-files-new
[2]: https://typescript-eslint.io/packages/typescript-eslint#migrating-from-legacy-config-setups
[3]: https://eslint.style/guide/getting-started
[4]: https://eslint.org/blog/2023/10/flat-config-rollout-plans/

eslint.config.js

@@ -0,0 +1,121 @@
+import eslint from "@eslint/js";
+import tseslint from "typescript-eslint";
+import stylistic from "@stylistic/eslint-plugin";
+
+export default tseslint.config(
+	{
+		// This block defines ignore patterns globally to all configurations below
+		// (therefore it can use slightly different patterns, see also the eslint "Flat Config" doc)
+		ignores: [
+			".husky/*",
+			".github/*",
+			".reuse/*",
+			"docs/*",
+			"rfcs/*",
+			"coverage/*",
+
+			// Exclude test files
+			"test/tmp/*",
+			"test/projects/*",
+			"test/fixtures/*",
+
+			// Exclude generated code
+			"lib/*",
+		],
+	},
+	// Base configs applying to JS and TS files
+	eslint.configs.recommended,
+	stylistic.configs.customize({
+		indent: "tab",
+		quotes: "double",
+		semi: true,
+		jsx: false,
+		arrowParens: true,
+		braceStyle: "1tbs",
+		blockSpacing: false,
+	}), {
+		// Lint all JS files using the eslint parser
+		files: ["**/*.js"],
+		languageOptions: {
+			ecmaVersion: 2022,
+			sourceType: "module",
+		},
+	}, {
+		// Lint all TS files using the typescript-eslint parser
+		// Also enable all recommended typescript-eslint rules
+		files: ["src/**/*.ts", "test/**/*.ts", "scripts/**/*.ts"],
+		extends: [
+			...tseslint.configs.recommendedTypeChecked,
+			...tseslint.configs.stylisticTypeChecked,
+		],
+		languageOptions: {
+			ecmaVersion: 2022,
+			sourceType: "module",
+			parser: tseslint.parser,
+			parserOptions: {
+				project: true,
+			},
+		},
+		rules: {
+			// TypeScript specific overwrites
+			// We must disable the base rule as it can report incorrect errors
+			"no-unused-vars": "off",
+			"@typescript-eslint/no-unused-vars": [
+				"error", {
+					argsIgnorePattern: "^_",
+					varsIgnorePattern: "^_",
+					caughtErrorsIgnorePattern: "^_",
+				},
+			],
+		},
+	}, {
+		// To be discussed: Type-aware checks might add quite some additional work when writing tests
+		// and could even require us to export types that we would otherwise not export
+		files: ["test/**/*.ts"],
+		rules: {
+			"@typescript-eslint/no-unsafe-argument": "off",
+			"@typescript-eslint/no-unsafe-assignment": "off",
+			"@typescript-eslint/no-unsafe-call": "off",
+			"@typescript-eslint/no-unsafe-enum-comparison": "off",
+			"@typescript-eslint/no-unsafe-member-access": "off",
+			"@typescript-eslint/no-unsafe-return": "off",
+			"@typescript-eslint/no-unsafe-unary-minus": "off",
+		},
+	}, {
+		// Overwrite any rules from the configurations above for both, JS and TS files
+		rules: {
+			"linebreak-style": [
+				"error",
+				"unix",
+			],
+			"@stylistic/object-curly-spacing": [
+				"error",
+				"never",
+			],
+			"@stylistic/operator-linebreak": ["error", "after"],
+			"@stylistic/comma-dangle": ["error", {
+				functions: "never",
+				arrays: "always-multiline",
+				objects: "always-multiline",
+				imports: "always-multiline",
+				exports: "always-multiline",
+				enums: "always-multiline",
+				generics: "always-multiline",
+				tuples: "always-multiline",
+			}],
+			"max-len": [
+				"error",
+				{
+					code: 120,
+					ignoreUrls: true,
+					ignoreRegExpLiterals: true,
+				},
+			],
+			"no-implicit-coercion": [
+				2,
+				{allow: ["!!"]},
+			],
+			"no-console": "error",
+		},
+	}
+);