Add Version method to NFT interface and implementation

Include `RunWithOutput` support in the command package and introduce version parsing logic, enabling retrieval of the nftables version and options.

internal/command/command.go

@@ -7,6 +7,7 @@ import (
 
 type NFT interface {
 	Run(arg ...string) error
+	RunWithOutput(arg ...string) (string, error)
 }
 
 type execNFT struct {
@@ -35,3 +36,15 @@ func (r *execNFT) Run(arg ...string) error {
 
 	return nil
 }
+
+func (r *execNFT) RunWithOutput(arg ...string) (string, error) {
+	cmd := exec.Command(r.nftPath, arg...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		if len(out) > 0 {
+			return string(out), err
+		}
+		return "", err
+	}
+	return string(out), nil
+}