Fixes #391

Add functionality to surf other user profiles and update user profile details.

* **User Profile Page (`lib/src/pages/home/profile.dart`)**
  - Add a new constructor parameter `user` to the `UserProfile` class to accept a `User` object.
  - Update the `getProfilePicture`, `build`, and `initState` methods to use the `user` parameter instead of `currentUser`.
  - Update various UI elements to display the `user` details instead of `currentUser`.

* **Global Leaderboard Page (`lib/src/pages/leaderboards/global_leaderboard.dart`)**
  - Update the `ListTile` widget to include an `onTap` callback that navigates to the `UserProfile` page with the selected user.

* **Monthly Leaderboard Page (`lib/src/pages/leaderboards/monthly_leaderboard.dart`)**
  - Update the `ListTile` widget to include an `onTap` callback that navigates to the `UserProfile` page with the selected user.

* **Issue Detail Page (`lib/src/pages/issues/issue_detail.dart`)**
  - Update the `Markdown` widget to include an `onTapLink` callback that navigates to the `UserProfile` page with the selected user.

* **State Provider (`lib/src/pages/sizzle/sizzle_state_provider.dart`)**
  - Add a new `StateProvider<User?>` to store the selected user for profile navigation.

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/OWASP-BLT/BLT-Flutter/issues/391?shareId=XXXX-XXXX-XXXX-XXXX).