[MattCCC]

This pull request undoes one change of #121, which saved a few bytes but made requests measurably slower. It targets the 4.3.0 release pull request #120.

🐛 Bug Fixes

• Custom fetcher responses are extended property by property again: Reduce the bundle size without changing behavior #121 replaced six assignments in prepareResponse() with one Object.assign() of an object literal, which allocates an extra object for every response. In a benchmark comparing the builds before and after Reduce the bundle size without changing behavior #121, fetchf() with config options and interceptors was 2.4% slower (the median of 8 rounds, alternating which build ran first). With this change it's back to +0.7%, which is within the noise.
• The rest of Reduce the bundle size without changing behavior #121 stays. Cache key generation got faster (+3% to +11% across runs), and fetchf() and buildConfig() were within the noise.

🧪 Tests

• All 895 tests pass with 100% coverage.

📦 Bundle Size

The bundles grow by about 10 bytes (brotli), e.g. browser/index.mjs from 7.97 kB to 7.98 kB. That's still 0.16 kB smaller than before #121, and the README's 8.9 KB for fetchff doesn't change.

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Generated by Claude Code

[github-actions]

size-limit report 📦

Path	Size
dist/browser/index.mjs	7.79 KB (+0.13% 🔺)
dist/browser/index.global.js	7.98 KB (+0.1% 🔺)
dist/node/index.js	7.96 KB (+0.14% 🔺)
dist/react/index.mjs	10.96 KB (+0.56% 🔺)
dist/react/index.js	11.78 KB (+0.11% 🔺)