Several issues about "ExperienceAttestations.sol"

[williamniu]

1. Permission Control: Right now, basically anyone can issue an attestation, which is great for openness, but it could easily turn into spam.
   So we probably need some kind of access control — maybe the owner sets specific roles, or we just keep a simple whitelist of approved issuers.
2. Revocation Details & Auditability: When an attestation gets revoked, we don’t really log anything besides the fact that it was revoked.
3. Scalability Issues: The "attestationOf" mapping just keeps growing forever, and over time it’ll get huge. If the frontend tries to load everything at once, it’ll choke.
4. Duplicate / Double-Issuance Prevention: Depending on the use case, we might want a “duplicate check” so the system won’t issue the same metadata to the same recipient twice.