fix: resolve golangci-lint warnings

- wrap flasher.Close() error in defer closure
- handle error return from SetReadTimeout()
- use explicit _ assignment for unused error
- remove redundant XOR in checksum test

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jgangemi

main.go

@@ -112,7 +112,11 @@ func main() {
 	if err != nil {
 		log.Fatalf("Failed to connect: %v", err)
 	}
-	defer flasher.Close()
+	defer func() {
+		if err := flasher.Close(); err != nil {
+			log.Printf("Warning: failed to close flasher: %v", err)
+		}
+	}()
 
 	fmt.Printf("Chip: %s\n", flasher.ChipName())
 

pkg/espflasher/flasher.go

@@ -963,5 +963,5 @@ type StdoutLogger struct {
 
 // Logf implements the Logger interface.
 func (l *StdoutLogger) Logf(format string, args ...interface{}) {
-	fmt.Fprintf(l.W, format+"\n", args...)
+	_, _ = fmt.Fprintf(l.W, format+"\n", args...)
 }

pkg/espflasher/protocol_test.go

@@ -22,7 +22,7 @@ func TestChecksum(t *testing.T) {
 		{
 			name:     "single byte zero",
 			data:     []byte{0x00},
-			expected: checksumMagic ^ 0x00,
+			expected: checksumMagic,
 		},
 		{
 			name:     "single byte 0xFF",

pkg/espflasher/slip.go

@@ -93,7 +93,9 @@ func (r *slipReader) ReadFrame(timeout time.Duration) ([]byte, error) {
 		}
 
 		readTimeout := min(remaining, 100*time.Millisecond)
-		r.port.SetReadTimeout(readTimeout)
+		if err := r.port.SetReadTimeout(readTimeout); err != nil {
+			return nil, fmt.Errorf("failed to set read timeout: %w", err)
+		}
 
 		n, err := r.port.Read(buf)
 		if err != nil && err != io.EOF {