chore: add jsdoc

lib/mod.ts

···
+/**
+ * represents an acquired lock that can be released
+ */
 export interface Lock extends Disposable {
 	dispose(): void;
 }
 
+/**
+ * provides mutual exclusion for async operations
+ */
 class Mutex {
 	#promise = Promise.resolve();
 
+	/**
+	 * acquires the mutex, blocking until available
+	 * @returns a lock that must be disposed to release the mutex
+	 */
 	async acquire(): Promise<Lock> {
 		const { promise, resolve } = Promise.withResolvers<void>();