fix(flock): add Windows stub for cross-platform build

Author: tyeongkim

internal/flock/flock_windows.go

@@ -0,0 +1,21 @@
+//go:build windows
+
+package flock
+
+import (
+	"fmt"
+	"os"
+)
+
+func Lock(path string) (func(), error) {
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0o644)
+	if err != nil {
+		return nil, fmt.Errorf("open lock file: %w", err)
+	}
+
+	unlock := func() {
+		f.Close()
+	}
+
+	return unlock, nil
+}