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

mfer/deserialize.go

@@ -26,7 +26,7 @@ func (m *manifest) deserializeInner() error {
 	if err != nil {
 		return err
 	}
-	defer gzr.Close()
+	defer func() { _ = gzr.Close() }()
 
 	dat, err := io.ReadAll(gzr)
 	if err != nil {
@@ -99,7 +99,7 @@ func NewManifestFromFile(fs afero.Fs, path string) (*manifest, error) {
 	if err != nil {
 		return nil, err
 	}
-	defer f.Close()
+	defer func() { _ = f.Close() }()
 	return NewManifestFromReader(f)
 }