[codex] Improve wifi_network table tests

[grahamgilbert]

Summary

• add deterministic command and osquery fakes for wifi_network tests
• cover disconnected Wi-Fi output, command failures, query errors, generator output, and wdutil parsing edge cases
• route WifiNetworkGenerate through an injectable helper while preserving production behavior

Tests

• rtk env GOCACHE=/tmp/osquery-extension-go-cache go test ./tables/wifi_network
• rtk env GOCACHE=/tmp/osquery-extension-go-cache go test ./...