Use default pnpm package import method

[sokra]

What?

Use pnpm's default package import method in the two hoisted isolated-test configurations added by #98425.

Why?

package-import-method controls how regular package files are materialized from pnpm's store: by reflink, hardlink, or copy. Those choices do not affect realpath, so forcing copies is unrelated to the Node.js symlink-resolution workaround and unnecessarily disables pnpm's more efficient defaults.

How?

Keep node-linker=hoisted, which is the setting responsible for producing npm-style real package directories, while removing the independent copy policy. The Node-version gate, local-tarball validation, release-age policy, and fixture behavior remain unchanged.

Verification

• Hoisted-only scratch install produced real package directories, no package symlinks outside .bin, and a metadata-only .pnpm
• Production Turbopack: non-hoisted SWC helper and warm-restart task stats passed (2/2)
• pnpm build
• pnpm types
• Prettier, ESLint, and git diff --check

Follow-up to #98425 and #98425 (comment).

[github-actions]

Tests Passed

Commit: 78d7964