fix: honor retry-after and disabled key state

[fengjikui]

Summary

• use provider retry-after values as the actual quarantine duration instead of only recording them
• keep permanently disabled keys out of the no-active-key fallback path, while still allowing quarantined keys to recover
• tighten a few Bun/fetch typings so the existing CI typecheck gate passes

Tests

• bun test src/state.test.ts
• bun test
• bun run typecheck
• git diff --check

[bulutmuf]

Hi @fengjikui, thank you so much for your contribution! 🎉

You caught two very critical bugs here (the retry-after duration being ignored, and disabled keys breaking the fallback loop).

I just published a major v2.0.0 refactor which completely changed the architecture and caused some merge conflicts with your PR. I am currently resolving the conflicts manually on my end to integrate your logic into the new architecture, while making sure to preserve your commit authorship.

I will get this merged shortly. Thanks again for the great catch!