CVE-2026-48795: @adonisjs/bodyparser has an incomplete fix for CVE-2026-25754

The fix for GHSA-f5x2-vj4h-vg4c / CVE-2026-25754 introduced in commit 40e1c71 is incomplete and can be bypassed through nested prototype pollution payloads.

The original patch replaced the internal FormFields storage object with Object.create(null), preventing direct payloads such as __proto__.polluted. However, payloads containing a non-dangerous segment before __proto__ or constructor.prototype, such as user.__proto__.polluted, still lead to Object.prototype pollution.

This issue is exploitable remotely through a single unauthenticated multipart/form-data request using the default configuration.