Excluded iPAddress name constraints with an all-zero mask are not applied

Summary

An `excluded_subtrees` iPAddress name constraint with an all-zero mask (`0.0.0.0/0` or `::/0`) does not restrict iPAddress SANs in certificates issued beneath it. The mask check treated an all-zero mask as matching nothing, when a `/0` prefix matches every address of its family, so the exclusion was silently ignored.

CA/Browser Forum Baseline Requirements §7.1.2.5.2 require exactly these exclusions on every technically constrained sub-CA that may not issue for IP addresses. As a result, anyone holding (or having compromised) the key of such a sub-CA can issue a certificate for an arbitrary IP address, and `Validator` with `RFC5280Policy` and `ServerIdentityPolicy` accepts it for that address. A `permitted_subtrees` dNSName entry on the same issuer does not prevent this, because iPAddress SANs are a different name form.

All users of `Validator` with `RFC5280Policy` are affected when a chain can contain a name-constrained issuer with an all-zero iPAddress exclusion.

The issue is fixed in x509-validator 0.3.1 (commit [da661f8](https://github.com/namecare/x509-validator/commit/da661f8ecee820e05d089a76ecb654ff52a2c987)). Users should upgrade to 0.3.1 or later.