Add adaptive response-header rate limiting

[TDanks2000]

What changed

• Adds a provider-neutral createHeaderRateLimitPlugin.
• Learns limit, remaining, reset time, and Retry-After values from response headers.
• Pauses later requests only after the server reports an exhausted budget or explicit retry delay.
• Supports Unix-second, Unix-millisecond, and relative-second reset headers.
• Exposes a read-only state snapshot for wrapper diagnostics.
• Keeps queued waits abortable and adds deterministic tests plus a minor Changeset.

Why

Static client-side budgets become inaccurate when an API temporarily lowers or changes its limits. Wrappers such as AniList can now follow the server's current headers without putting provider-specific behavior into the core runtime.

Validation

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