[Medium] Implement Access Control contract

[Josie123-Dev]

Task Description

Create Access Control contract for credentials:

• Manage access permissions
• Control credential access
• Implement time-based access
• Add access revocation
• Track access logs

Requirements

• Permission management
• Access control
• Time-based access
• Revocation logic
• Access logging

Acceptance Criteria

• Permissions work
• Access is controlled
• Time limits work
• Revocation works
• Access is logged

[Williams-1604]

I'm relatively early in my journey with Soroban, but I've studied the codebase for Validfi and I believe I can handle this issue with care and attention to detail. I'd really appreciate the chance to prove myself here — I won't let the project down. Just like i did a perfect job last wave with no failing CI pipeline. Kindly consider my application please.

[grantfox-oss]

🦊 GrantFox — @Williams-1604 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #87)
2. Your PR will be reviewed by the GuardZero144 maintainers

Good luck! Track your progress on GrantFox.