🔒 Fix TOCTOU SSRF Vulnerability in URL Fetching

[Tcode-Motion]

🎯 What: Removed preemptive DNS resolution and IP checking from is_safe_url. IP validation now happens exclusively in SafeResolver during the actual connection attempt in ureq.

⚠️ Risk: Time-of-Check to Time-of-Use (TOCTOU) vulnerability where an attacker could bypass SSRF protections using DNS rebinding, returning a safe IP during initial validation and an internal IP during the subsequent connection.

🛡️ Solution: is_safe_url now solely verifies the scheme and URL structure. By shifting all DNS resolution and IP filtering to the connection phase within ureq's SafeResolver, we ensure the IP validated is the exact one being connected to, preventing the TOCTOU attack vector.

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PR created automatically by Jules for task 1000401122315601984 started by @Tcode-Motion

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