feat!: create levels as a tuple

This might be a little bit more useful in usage than an array, especially where code might require a tuple as argument. As `levels` was recently introduced there is likely very little impact of this change, regardless, it is a breaking change.

src/bunyan/levels.test.ts

@@ -1,6 +1,19 @@
 import test from 'ava';
+import {type LogLevelString} from 'bunyan';
 import levels from './levels.js';
 
 test('contains all Bunyan levels', (t) => {
   t.deepEqual(levels, ['trace', 'debug', 'info', 'warn', 'error', 'fatal']);
 });
+
+const isValidLevel = test.macro<[(typeof levels)[number]]>({
+  exec(t, level) {
+    const bunaynLevel: LogLevelString = level;
+    t.is(level, bunaynLevel);
+  },
+  title: (_, level) => `"${level} is a valid Bunyan level`,
+});
+
+for (const level of levels) {
+  test(isValidLevel, level);
+}

src/bunyan/levels.ts

@@ -1,12 +1,3 @@
-import {type LogLevelString} from 'bunyan';
-
-const levels: readonly LogLevelString[] = [
-  'trace',
-  'debug',
-  'info',
-  'warn',
-  'error',
-  'fatal',
-] as const;
+const levels = ['trace', 'debug', 'info', 'warn', 'error', 'fatal'] as const;
 
 export default levels;