[codex] Improve localnetworkpermissions table tests

[grahamgilbert]

Summary

• add generator coverage using a temporary network extension plist path
• cover missing and invalid plist behavior
• add object extraction, UID resolution, and non-permission dictionary edge cases

Validation

• GOCACHE=/tmp/osquery-extension-go-cache go test ./tables/localnetworkpermissions
• GOCACHE=/tmp/osquery-extension-go-cache go test ./...