[codex] Improve macosrsr table tests

[grahamgilbert]

Summary

• add macosrsr column and generator coverage
• make SystemVersion.plist reads and sw_vers calls injectable for deterministic tests
• cover unsupported macOS versions, sw_vers failures, invalid versions, and invalid plist input

Validation

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