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/freshen.go

@@ -258,7 +258,7 @@ func (mfa *CLIApp) freshenManifestOperation(ctx *cli.Context) error {
 					}
 				}
 			})
-			f.Close()
+			_ = f.Close()
 
 			if err != nil {
 				return fmt.Errorf("failed to hash %s: %w", e.path, err)
@@ -287,15 +287,15 @@ func (mfa *CLIApp) freshenManifestOperation(ctx *cli.Context) error {
 	}
 
 	err = builder.Build(outFile)
-	outFile.Close()
+	_ = outFile.Close()
 	if err != nil {
-		mfa.Fs.Remove(tmpPath)
+		_ = mfa.Fs.Remove(tmpPath)
 		return fmt.Errorf("failed to write manifest: %w", err)
 	}
 
 	// Rename temp to final
 	if err := mfa.Fs.Rename(tmpPath, manifestPath); err != nil {
-		mfa.Fs.Remove(tmpPath)
+		_ = mfa.Fs.Remove(tmpPath)
 		return fmt.Errorf("failed to rename manifest: %w", err)
 	}