Replace 6 unwrap() calls with safe error handling in DQN IQN code:
- Production: 3 unwrap() on iqn_network/iqn_target_network replaced with
ok_or_else returning MLError::ModelError for clear diagnostics
- Tests: 2 result.unwrap() replaced with ?, 2 DQN::new().unwrap() replaced
with ? after changing test signatures to return anyhow::Result<()>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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