feat-add theme toggle button

[santhos-13]

closes #291

Changes proposed

Added a reusable toggle button component that toggles between light and dark mode.

Check List (Check all the applicable boxes)

• [x] My code follows the code style of this project
• [x] All new and existing tests passed.
• [x] This PR does not contain plagiarized content.
• [x] The title of my pull request is a short description of the requested changes.

[santhos-13]

@biratdatta