network: fix GetFreeIp limit across multiple ranges

[tllovesxs]

Summary

• Fix the remaining GetFreeIp limit calculation across multiple IP ranges.
• Stop processing once the remaining limit is zero, including limit=0.

Fixes #29.

Test plan

• git diff --check
• Review the multi-range path in L3BasicNetwork.handle(APIGetFreeIpMsg).
• The full integration test requires the project test environment (database and simulator), so it was not run locally.

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[zsphere-opensource]

Thanks for the detailed report and the proposed fix.
The change appears to address the remaining-limit calculation across multiple IP ranges. We’ll evaluate the implementation and validate the relevant behavior through our internal review process, including IPv4, IPv6, and multiple-range cases.
If the validation passes and the change is approved, we’ll integrate it through our internal GitLab workflow and synchronize the accepted commit back to the public repository while preserving your authorship.
We’ll update this PR after the evaluation is complete.