First release.

• Client for the ITOC360 Events API with bearer token authentication
• send_alert for Alertmanager-compatible sources (prometheus, mimir,
  cortex, loki, signoz, grafana)
• send_raw for every other provider
• Typed errors: APIError with unauthorized, subscription_inactive and
  retryable; ValidationError for locally rejected alerts
• Ships py.typed for mypy and pyright
• No dependencies outside the standard library