refactor: decouple fingerprinting from executor (#1039)

internal/fingerprint/sources.go

@@ -0,0 +1,16 @@
+package fingerprint
+
+import "fmt"
+
+func NewSourcesChecker(method, tempDir string, dry bool) (SourcesCheckable, error) {
+	switch method {
+	case "timestamp":
+		return NewTimestampChecker(tempDir, dry), nil
+	case "checksum":
+		return NewChecksumChecker(tempDir, dry), nil
+	case "none":
+		return NoneChecker{}, nil
+	default:
+		return nil, fmt.Errorf(`task: invalid method "%s"`, method)
+	}
+}