PYSEC-2026-3564 datamodel-code-generator vulnerable to SSRF via --url: no host/IP validation, follows redirects

Summary datamodel-code-generator's built-in HTTP fetcher http.getbody issues an httpx.GET against any URL passed to --url or reached via a redirect chain with no allow-list, no deny-list, no IP/host validation, and followredirects=True. Loopback addresses, RFC1918 ranges, link-local 169.254.169.2...