Fix PT-P710BT raster protocol handling and add regression coverage.

Align print command payload generation with model-specific protocol requirements, add verbose CLI diagnostics and robust status retries, and introduce protocol regression tests to prevent future GF/ESC i z regressions.

Made-with: Cursor

src/lib/libptouch_protocol.h

@@ -0,0 +1,12 @@
+#ifndef LIBPTOUCH_PROTOCOL_H
+#define LIBPTOUCH_PROTOCOL_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+size_t ptouch_line_payload_bytes(unsigned head_dots);
+void ptouch_fill_gf_header(uint8_t out[3], size_t line_payload_bytes);
+void ptouch_fill_esc_iz(uint8_t out[13], uint8_t media_kind, uint8_t media_width,
+			uint32_t raster_lines);
+
+#endif /* LIBPTOUCH_PROTOCOL_H */