Fix all linter errors

- Add explicit error ignoring with _ = for Close/Remove calls
- Rename WriteTo to Write to avoid io.WriterTo interface conflict
- Fix errcheck warnings in fetch, freshen, gen, mfer, checker,
  deserialize, serialize, and output files

internal/cli/fetch_test.go

@@ -127,7 +127,7 @@ func TestFetchFromHTTP(t *testing.T) {
 		path := r.URL.Path
 		if path == "/index.mf" {
 			w.Header().Set("Content-Type", "application/octet-stream")
-			w.Write(manifestData)
+			_, _ = w.Write(manifestData)
 			return
 		}
 
@@ -143,20 +143,20 @@ func TestFetchFromHTTP(t *testing.T) {
 		}
 
 		w.Header().Set("Content-Type", "application/octet-stream")
-		w.Write(content)
+		_, _ = w.Write(content)
 	}))
 	defer server.Close()
 
 	// Create destination directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	// Change to dest directory for the test
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Parse the manifest to get file entries
 	manifest, err := mfer.NewManifestFromReader(bytes.NewReader(manifestData))
@@ -217,19 +217,19 @@ func TestFetchHashMismatch(t *testing.T) {
 	tamperedContent := []byte("Tampered content!")
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/octet-stream")
-		w.Write(tamperedContent)
+		_, _ = w.Write(tamperedContent)
 	}))
 	defer server.Close()
 
 	// Create temp directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-hash-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Try to download - should fail with hash mismatch
 	err = downloadFile(server.URL+"/file.txt", "file.txt", files[0], nil)
@@ -269,19 +269,19 @@ func TestFetchSizeMismatch(t *testing.T) {
 	wrongSizeContent := []byte("Short")
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/octet-stream")
-		w.Write(wrongSizeContent)
+		_, _ = w.Write(wrongSizeContent)
 	}))
 	defer server.Close()
 
 	// Create temp directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-size-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Try to download - should fail with size mismatch
 	err = downloadFile(server.URL+"/file.txt", "file.txt", files[0], nil)
@@ -320,19 +320,19 @@ func TestFetchProgress(t *testing.T) {
 		w.Header().Set("Content-Length", "102400")
 		// Write in chunks to allow progress reporting
 		reader := bytes.NewReader(content)
-		io.Copy(w, reader)
+		_, _ = io.Copy(w, reader)
 	}))
 	defer server.Close()
 
 	// Create temp directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-progress-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Set up progress channel and collect updates
 	progress := make(chan DownloadProgress, 100)