feat: implement rate limiting and anti-spam for bets and events

[greatest0fallt1me]

Description:

Implement configurable rate limiting (e.g., max bets per user per time window, max events per admin) to reduce spam and abuse.

Requirements and Context:

• Must be secure, tested, and documented
• Should allow admin to set rate limits (e.g., per user per event or global)
• Should enforce limits in place_bet and optionally in create_event
• Should use time windows (e.g., last N ledger closes or seconds)
• Should emit clear error when limit exceeded
• Must not block legitimate high-volume use with reasonable limits

Suggested Execution:

1. Fork the repo and create a branch

   git checkout -b feature/rate-limiting

2. Implement changes

   • Write contract: src/lib.rs (rate limit checks)
   • Add rate_limiter module: src/rate_limiter.rs
   • Update storage and validation; add documentation and NatSpec-style comments

3. Test and commit

   • Run tests; cover at limit, over limit, window expiry
   • Include test output and security notes

Example Commit Message:

feat: implement rate limiting and anti-spam for bets and events

Guidelines:

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 72 hours