feat(core): add per-request cache TTL and override options

[Andrchiamus]

Summary

• Add cacheTTL and cacheOverrides options to get() for per-request cache configuration, following the same override pattern used by retry
• Extract CacheOverrideOptions into a reusable exported interface (previously inline in HttpClientOptions)
• Shallow-merge semantics: per-request fields override constructor fields, unspecified fields fall back to constructor defaults
• Threaded through all cache paths: fresh store, 304 refresh, SWR background revalidation, ignoreNoStore, ignoreNoCache

Usage

// Override TTL for a specific request
await client.get(url, { cacheTTL: 120 });

// Override cache behavior for a specific request
await client.get(url, {
  cacheOverrides: { ignoreNoStore: true, minimumTTL: 60 },
});

// Combine both
await client.get(url, {
  cacheTTL: 300,
  cacheOverrides: { maximumTTL: 600 },
});

Test plan

• cacheTTL overrides defaultCacheTTL (no cache headers → uses request TTL)
• Per-request minimumTTL overrides constructor minimumTTL
• Per-request maximumTTL overrides constructor maximumTTL
• Per-request ignoreNoStore: true forces caching despite no-store
• Per-request ignoreNoCache: true skips revalidation
• Shallow merge — unspecified per-request fields fall back to constructor
• Per-request overrides apply on 304 refresh path
• Per-request cacheTTL applies in backgroundRevalidate (SWR path)
• No per-request options → unchanged constructor behavior (regression)
• TypeScript compiles cleanly
• All 265 existing + new tests pass

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