refactor: migrate 'flowutils' to 'must' helpers

pkg/must/must.go

@@ -0,0 +1,27 @@
+package must
+
+import (
+	"fmt"
+	"io"
+)
+
+func Do(err error) {
+	if err != nil {
+		panic(err)
+	}
+}
+
+func Get[T any](val T, err error) T {
+	Do(err)
+	return val
+}
+
+func Be(condition bool, msg string, args ...any) {
+	if !condition {
+		panic(fmt.Errorf(msg, args...)) //nolint:err113 // not a returned error
+	}
+}
+
+func Close(closer io.Closer) {
+	Do(closer.Close())
+}