refactor: Updated class modifiers, added Lottie animations, and reorganized pubspec dependencies

[utpal-barman]

General

• Modified class access levels for better structure.
• Integrated Lottie animations.
• Grouped and reorganized dependencies in the pubspec.yaml for improved readability.

Checklists

• Platform specific changes (input, image picking etc) are tested on both of the platforms (Android and iOS)
• It is tested that the UI changes are rendered correctly on different device sizes (such as long lists or expanded rows) with safe area conditions.
• Edge cases, such as responses being empty or invalid, missing data, no internet connection etc, are tested and the app works as expected.

Showcase

• Either showcase screenshots / videos are attached, or this PR does not require such any showcase.