fs: `walkSync` returns a type without iterator helpers

**Describe the bug** `walkSync` returns `IterableIterator<WalkEntry>`, which doesn't implement iterator helper methods. However it's implemented as a generator function so it has them at the runtime. **Steps to Reproduce** ```ts const a = walkSync("."); const b = a.map(v => v.name); // Property 'map' does not exist on type 'IterableIterator<WalkEntry>'. ``` **Environment** <!-- please complete the following information --> - OS: Windows 10 - deno version: deno 2.7.11 - std version: 1.0.23