Unbounded memory consumption via MIME-header limit bypass

Memory-limit bypass in Go mime/multipart allows attackers to consume unbounded memory via crafted multipart forms. MIME-header parsing in net/textproto reads an arbitrarily long input line despite the form's memory budget when less than 400 bytes remain at the start of a part. Exposure requires an application to parse attacker-controlled multipart forms; the disclosed consequence is excessive memory allocation, with no specific crash or hang outcome documented.