Replace load.sh with Go program

lib/picotool/picotool.go

@@ -0,0 +1,24 @@
+package picotool
+
+import (
+	"fmt"
+	"os/exec"
+)
+
+func Load(uf2Path string) error {
+	cmd := exec.Command("picotool", "load", "-f", uf2Path)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("picotool load: %w\n%s", err, out)
+	}
+	return nil
+}
+
+func Reboot() error {
+	cmd := exec.Command("picotool", "reboot")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("picotool reboot: %w\n%s", err, out)
+	}
+	return nil
+}