### Description of Change

This PR addresses the need for fragments/hashes to be treated as
first-party parameters within the `go_router` package, as highlighted in
[issue #150155](https://github.com/flutter/flutter/issues/150155).
Previously, users had to manually append the fragment to the URL, which
could lead to potential bugs. With this update, the `fragment` is now a
dedicated parameter, allowing for a more seamless and bug-free
integration.

#### Before:

```dart
final location = context.namedLocation('some_route'); // const nested records
// Manually adding the fragment, hoping there aren't any weird bugs surrounding it
context.replace('$location#https://a.url/that?i=mightuse');
```

#### After:

```dart
// Directly passing the fragment as a parameter
context.goNamed("details", fragment: 'https://a.url/that?i=mightuse');

// or

final location = GoRouterState.of(context).namedLocation(
  'details',
  fragment: 'section3',
);
context.go(location);

// or 

final location = context.namedLocation(
 'details',
 fragment: 'section3',
);
context.go(location);
```

### Issues Fixed

This PR resolves [issue
#150155](https://github.com/flutter/flutter/issues/150155).

---

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