feature/alphavantage-provider-rate-limit-handling

AlphaVantage provider currently does not have explicit rate limit handling. Free tier accounts are limited to 5 calls per minute and 500 per day. This issue tracks the implementation of a more robust rate limiting and retry mechanism for the AlphaVantage data provider.

Tasks

• [ ] Implement rate limit tracking for AlphaVantage (5 calls/min).
• [ ] Add exponential backoff or waiting logic when 429 errors are encountered.
• [ ] Document the rate limit constraints in the config or provider documentation.
• [ ] (Optional) Add support for daily limit tracking (500/day).