[Easy] Implement credential batch operations

[Josie123-Dev]

Task Description

Add batch operations for credentials in contracts:

• Batch credential issuance
• Batch credential verification
• Batch credential update
• Batch credential deletion
• Emit batch events

Requirements

• Batch issuance
• Batch verification
• Batch update
• Batch deletion
• Batch events

Acceptance Criteria

• Batch issuance works
• Batch verification works
• Batch update works
• Batch deletion works
• Batch events are emitted