TypeError: file name contained an unexpected NUL byte: lstat occurs when trying to cache a specific URL.

This was quite an interesting error.
The cause of this error was that SHA-256 generated output containing a null byte.

## detail

The following error occurred only when trying to cache a specific URL: e.g. https://esm.sh/stable/react@18

```
Uncaught (in promise) TypeError: file name contained an unexpected NUL byte: lstat '/�g��E=m�Y:M���t ���-�Ƀ�c���j'
```

Here’s the minimal code to reproduce the issue:

```ts
import { cache } from "jsr:@denosaurs/cache@0.2.15";

const ns = "";
const url = "https://esm.sh/stable/react@18";
const fs = await cache(url, undefined, ns);
console.log("cached: %o %o", fs.path, fs.meta);
```

The error occurred only when providing `react@18` to esm.sh, so I assume this was an error I encountered probabilistically. Since I found it intriguing, I decided to investigate further.

It seems that, depending on the combination of SHA256 and input used in the process of computing the file name for cache storage, a NUL byte is unintentionally included.

Here's a version of the code with fewer dependencies:

```ts
// pick from https://github.com/denosaurs/cache/blob/83e4287694b0affe39bcad72f4cb7f99d3679057/file.ts#L125
async function hash(url: URL): Promise {
const formatted = `${url.pathname}${url.search ? "?" + url.search : ""}`;
const encoder = new TextEncoder();
const data = encoder.encode(formatted);
const hash = await crypto.subtle.digest("SHA-256", data);
return new TextDecoder().decode(hash);
}

// await Deno.lstat("hello\0world"); // same error is occurred

const url = "https://esm.sh/stable/react@18";
const calculatedPath = await hash(new URL(url));
console.log("calculated path", calculatedPath);
console.log("has null byte?", calculatedPath.includes("\0")); // true
console.log(await Deno.lstat(calculatedPath)); // same error is occurred
```