Fix rate limit validation error for unlimited accounts

[jmazzahacks]

Summary

Fixes a Pydantic validation error that occurs when the OpenRouter API returns requests: -1 to indicate unlimited rate limits.

Problem

The client encounters validation errors when OpenRouter returns -1 for unlimited accounts:

ERROR:openrouter_client.http: Failed to set rate limit: 1 validation error for RateLimit
max_requests
  Input should be greater than or equal to 1 [type=greater_than_equal, input_value=-1, input_type=int]

Solution

Added a simple check in _initialize_rate_limit() to skip rate limit configuration when requests <= 0:

# Handle special case where requests = -1 (unlimited/no limit)
if int(requests) <= 0:
    self.logger.debug(f"API returned unlimited rate limit (requests={requests}), skipping rate limit configuration")
    return

Testing

Confirmed the fix resolves the validation errors for unlimited accounts while maintaining functionality for standard rate-limited accounts.

Contributed by @jmazzahacks