Bug: useScan() ignores `enabled: false` and always starts scanning

## Description

`useScan()` unconditionally calls `start()` regardless of the `enabled` option, unlike `scan()` which properly guards against it.

```ts
// scan() — respects enabled ✅
export const scan = (options: Options = {}) => {
setOptions(options);
if (options.enabled === false && options.showToolbar !== true) {
return;
}
start();
};

// useScan() — ignores enabled ❌
export const useScan = (options: Options = {}) => {
setOptions(options);
start(); // always runs regardless of enabled
};
```

## Reproduction

```tsx
import { useScan } from "react-scan";

function App() {
useScan({ enabled: false }); // scanning still activates
return

;
}
```

## Expected Behavior

When `enabled: false` is passed to `useScan()`, scanning and the toolbar should not activate — matching the behavior of `scan()`.

## Related

- #269 — "scan is always enabled as long as showToolbar is true" (closed but a commenter confirmed still broken in 0.3.3)
- #101 — Added the `enabled` guard to `scan()` but never applied it to `useScan()`

## Proposed Fix

Apply the same iframe and `enabled` guards from `scan()` to `useScan()`:

```ts
export const useScan = (options: Options = {}) => {
setOptions(options);
const isInIframe = Store.isInIframe.value;

if (
isInIframe &&
!ReactScanInternals.options.value.allowInIframe &&
!ReactScanInternals.runInAllEnvironments
) {
return;
}

if (options.enabled === false && options.showToolbar !== true) {
return;
}

start();
};
```

Branch with the fix: https://github.com/jalbarrang/react-scan/tree/fix/usescan-respects-enabled

> _Note: Unable to open a PR since the repo restricts PRs to collaborators._