Add CEL validation tests for CRDs

[TheBeeZee]

Adds test cases under pkg/crdtest/testdata/ to verify CEL validation rules for ClusterNetworkPolicy (v1alpha2):

• Valid/Invalid CIDRs: Verifies IPv4/IPv6 CIDR format validation.
• Port Ranges: Verifies that start < end constraint is enforced (e.g., rejecting 80-80).
• Egress Constraints (Experimental): Verifies mutual exclusion between egress peers (egress.to) and destination named ports.
  • Note: Experimental test cases (named *.experimental.yaml) are automatically skipped by default when running against standard CRDs, as the validation rules are not present.

Fixes: #148

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[k8s-ci-robot]

Hi @TheBeeZee. Thanks for your PR.

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[danwinship]

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[danwinship]

/ok-to-test
/approve

I'll leave it for someone else to lgtm.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: danwinship, TheBeeZee

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