Implement Rate Limiting and Throttling

[DevMuhdishaq]

Description

Add rate limiting and throttling mechanisms to prevent abuse and ensure stable contract operation under high transaction volume.

Acceptance Criteria

• Rate limiter configuration with customizable limits
• Per-account transaction rate tracking
• Throttling logic that delays excessive requests
• Whitelist functionality for trusted addresses
• Admin function to adjust rate limits
• Metrics collection for monitoring (transaction counts, delays)
• Tests covering normal, edge, and abuse scenarios

Tasks

1. Design rate limiting algorithm
2. Implement transaction tracking
3. Add throttling delay calculation
4. Create whitelist management
5. Implement metrics logging
6. Write stress tests