`datasette-ip-rate-limit` `0.1a0`, path-level IP throttling for crawler abuse

Bad crawlers hitting hot paths can now be blocked with 60 req/60s per-rule limits. Path-specific throttling in datasette.yml makes this a practical low-cost ops guardrail.

• —Production config reads Fly-Client-IP and sets max_keys to 10000. It fits proxy-based deployments without extra app logic.
• —Exemptions for /static/* and /-/turnstile* keep assets and bot checks flowing while narrowing protection to expensive routes.
• —The example rule targets /global-power-plants/* and /legislators/*: 60 requests per 60s, then 20s blocked.
• —Still an alpha at 0.1a0, but the config surface is small enough to copy into lightweight self-hosted services quickly.