rivals-api 5.1.0

• Pace HTTP/browser API requests per provider across clients in the same process.
  Honor HTTP 429 Retry-After seconds/date headers, otherwise back off from
  30 seconds up to five minutes. Cooldown requests fail locally with
  status_code and retry_after; cached provider responses remain usable.
  Add optional request_interval and rate_limit_cooldown client settings.
• Prevent normal overall/hero/class lookups from repeating fully failed
  calculations within five seconds or continuing calls to a rate-limited source
  in the same calculation. Other providers still supply available summaries.

Validation: 215 tests pass; Ruff and package build pass. Live RivalsData check confirmed two attempts generated only one upstream request after HTTP 429.