Improve linting

[PearlGrell]

Description

The current code contains several areas that require modernization and cleanup:

• Deprecated usage of methods like withOpacity instead of withAlpha
• Use of BuildContext across async functions without checking context.mounted
• Presence of unused variables
• Unnecessary null checks

Solution

• Replace deprecated methods (e.g., withOpacity) with updated alternatives like withAlpha
• Introduce context.mounted checks in asynchronous methods
• Remove unused variables
• Remove the unnecessary null checks

Please assign GSSoC 2025 label and a level

[Robinbinu]

Hey @PearlGrell, excited to have you onboard! you've been assigned to this issue as requested