Remote server bundle duplicates concurrent collection downloads

When several server API requests ask for different icons from the same cold remote collection, each request starts its own full collection download. The cache is assigned only after fetch(...).json() resolves, leaving concurrent callers uncached.

In a production Node server with 20 overlapping API requests and a 49,940-byte synthetic collection, the current package makes 20 origin requests and transfers 998,800 uncompressed body bytes. Sharing the pending fetch reduces this to one request and 49,940 bytes.

Minimal reproduction: https://github.com/onmax/repros/tree/repro/nuxt-icon-perf-remote-collection-dedup/nuxt-icon-perf-remote-collection-dedup

git clone --depth 1 --branch repro/nuxt-icon-perf-remote-collection-dedup https://github.com/onmax/repros.git nuxt-icon-repro
cd nuxt-icon-repro/nuxt-icon-perf-remote-collection-dedup
npx --yes --package=node@24.19.0 --package=pnpm@11.15.1 --call 'pnpm install --frozen-lockfile && pnpm verify'
cd ../nuxt-icon-perf-remote-collection-dedup-fix
npx --yes --package=node@24.19.0 --package=pnpm@11.15.1 --call 'pnpm install --frozen-lockfile && pnpm verify'

The fixed fixture contains a pnpm patch and expects exactly one cold download. Both fixtures also verify warm caching, retry after a fetch/JSON failure, and retry after a falsey JSON result.

Run the linked repro's original and fixed fixtures with the provided Node and pnpm commands, then compare their verification results. The fix is done when concurrent requests produce exactly one cold collection download while warm caching works and fetch/JSON, including falsey JSON, failures can be retried.