Fix all golangci-lint errcheck and unused warnings

- Wrap defer resp.Body.Close() to capture error
- Ignore json.Unmarshal error in valueAny (best-effort)
- Check enc.Encode and os.Stdout.Write return values
- Check json.NewEncoder.Encode and w.Write in test helpers
- Check os.MkdirAll and os.WriteFile errors in tests
- Check first writeDefaultConfig() call in AlreadyExists test
- Remove unused mustMarshal helper

main.go

@@ -150,7 +150,7 @@ func queryPuppetDB(puppetDBURL, query string) ([]fact, error) {
 	if err != nil {
 		return nil, fmt.Errorf("request failed: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
@@ -176,7 +176,7 @@ func valueString(raw json.RawMessage) string {
 
 func valueAny(raw json.RawMessage) interface{} {
 	var v interface{}
-	json.Unmarshal(raw, &v)
+	_ = json.Unmarshal(raw, &v)
 	return v
 }
 
@@ -280,7 +280,7 @@ func run(cfg config, nodeName, factName, match, partialMatch string, showRole, n
 		enc := json.NewEncoder(os.Stdout)
 		enc.SetIndent("", "  ")
 		enc.SetEscapeHTML(false)
-		enc.Encode(hostFactMap)
+		_ = enc.Encode(hostFactMap)
 
 	case count:
 		values := stdinLines
@@ -299,7 +299,7 @@ func run(cfg config, nodeName, factName, match, partialMatch string, showRole, n
 			"all": map[string]interface{}{"hosts": hosts},
 		}
 		b, _ := yaml.Marshal(inventory)
-		os.Stdout.Write(b)
+		_, _ = os.Stdout.Write(b)
 
 	case nodeOnly:
 		for _, line := range returnData {