Add Checksums to Firmware & External App images (#1809)

* Pad image to 1MB and add simple checksum

* Test code to verify firmware checksum

* Comment out unneeded zlib

* Add files via upload

* Print space remaining in ROM

* Append checksum to external apps too

* Check external app checksums when loading

* Is it 2024 already?!

* Validate firmware checksum before flashing

* Add files via upload

* Added flash error warning to nav screen

* Clang

* Replaced some hard-coded values with #defines

* Check FW checksum before USB serial flash too

* Add files via upload

firmware/application/usb_serial_shell.cpp

@@ -41,6 +41,7 @@
 #include "chprintf.h"
 #include "chqueues.h"
 #include "ui_external_items_menu_loader.hpp"
+#include "ui_flash_utility.hpp"
 #include "untar.hpp"
 #include "ui_widget.hpp"
 
@@ -170,7 +171,13 @@ static void cmd_flash(BaseSequentialStream* chp, int argc, char* argv[]) {
     } else if (strEndsWith(path.native(), u".bin")) {
         // nothing to do for this case yet.
     } else {
-        chprintf(chp, "error only .bin or .ppfw.tar files canbe flashed.\r\n");
+        chprintf(chp, "error only .bin or .ppfw.tar files can be flashed.\r\n");
+        nav->pop();
+        return;
+    }
+
+    if (!ui::valid_firmware_file(path.native().c_str())) {
+        chprintf(chp, "error corrupt firmware file.\r\n");
         nav->pop();
         return;
     }