multiparty vulnerable to ReDoS via filename parsing

### Impact multiparty@4.2.3 and lower versions are vulnerable to denial of service via regular expression backtracking in the `Content-Disposition` filename parameter parser. A multipart upload with a long header value containing `!filename="1` repeated can cause regex matching to take seconds, blocking the event loop. Any service accepting multipart uploads via multiparty is affected. ### Patches Users should upgrade to multiparty@4.3.0 or higher. ### Workarounds None. Limiting upload sizes at the proxy/gateway layer reduces but does not eliminate the attack surface, since a small ~8 KB header is sufficient to trigger the vulnerable backtracking. ### Resources - [OWASP: Regular expression Denial of Service (ReDoS)](https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS)