🔒 Fix missing Network capability check in std.dns

[Tcode-Motion]

🎯 What:
Added a missing capability check for Capability::Network in stdlib/src/dns.rs within the lookup function. Also updated required_capabilities in the register_module call to accurately reflect this requirement.

⚠️ Risk:
Without this check, the system allowed any code, regardless of granted capabilities, to perform network DNS lookups. This could be exploited to bypass network restrictions, leak internal network structures, or act as a stepping stone for DNS-based attacks.

🛡️ Solution:
Replaced _ctx with ctx to evaluate capability configuration in the callback and inserted a conditional check that returns a RuntimeError (InvalidOperation) if ctx.config.capabilities.contains(&Capability::Network) evaluates to false. Validated the fix via a new deterministic integration test targeting restricted runtime environments.

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PR created automatically by Jules for task 15487683922587520007 started by @Tcode-Motion

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