utils: fix IPv4 /0 netmask conversion

[tllovesxs]

Summary

• Handle the IPv4 /0 netmask without a Java shift-by-32 error.
• Reject prefix lengths outside the IPv4 range.
• Add boundary and invalid-input unit tests.

Fixes #31.

Test plan

• git diff --check
• Added TestNetworkUtilsEdgeCases covering prefixes 0, 1, 24, 32, and an invalid prefix.
• The full Maven build is currently blocked in this environment by the repository's existing JAXB dependency issue on JDK 24.

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[zsphere-opensource]

Thanks for the detailed report and the proposed fix.
The change correctly handles the /0 case and validates the IPv4 prefix range before performing the shift. The added boundary tests for /0, /1, /24, and /32 are helpful.
Before we complete the evaluation, please also add test coverage for null and negative prefix values, since both are rejected by the new validation logic.
We’ll review and validate the change through our internal workflow. If the validation passes and the change is approved, we’ll integrate it internally and synchronize the accepted commit to the public repository while preserving your authorship.
We’ll update this PR after the evaluation is complete.