New VA108xx Rust workspace structure + dependency updates

- The workspace is now a monorepo without submodules. The HAL, PAC and BSP
  are integrated directly
- Update all dependencies: embedded-hal v1 and RTIC v2

va108xx-hal/tests/DueSerialTest/src/main.cpp

@@ -0,0 +1,78 @@
+#include <Arduino.h>
+
+enum SendModes {
+  ECHO,
+  ONLY_WRITE,
+  ONLY_READ,
+  WRITE_READ
+};
+
+enum StringModes {
+  FIXED,
+  VARIABLE
+};
+
+// Configure the test application here
+SendModes SEND_MODE = SendModes::WRITE_READ;
+StringModes STRING_MODE = StringModes::VARIABLE;
+uint8_t STRING_IDX = 0;
+
+String STRINGS[4] = {
+  "$Hi\n",
+  "$Hello\n",
+  "$Hello World\n",
+  "$Hello and Merry Christmas to all of you!\n"
+};
+
+void setup() {
+  // put your setup code here, to run once:
+  Serial.begin(115200);
+  Serial.println("Starting Arduino Serial Test script..");
+  Serial1.begin(115200);
+  if(STRING_MODE == StringModes::VARIABLE) {
+    STRING_IDX = 0;
+  }
+  pinMode(LED_BUILTIN, OUTPUT);
+}
+
+void loop() {
+  static byte ICOMING_BYTE = 0;
+  static uint32_t GLOBAL_IDX = 0;
+  digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
+  // put your main code here, to run repeatedly:
+  // send data only when you receive data:
+  if (SEND_MODE == SendModes::ONLY_WRITE or SEND_MODE == SendModes::WRITE_READ) {
+    Serial.println("Sending string..");
+    Serial1.write(STRINGS[STRING_IDX].c_str());
+    if(STRING_MODE == StringModes::VARIABLE) {
+      STRING_IDX += 1;
+      if(STRING_IDX > 3) {
+        STRING_IDX = 0;
+      }
+    }
+  }
+  if(
+    SEND_MODE == SendModes::WRITE_READ or
+    SEND_MODE == SendModes::ONLY_READ or
+    SEND_MODE == SendModes::ECHO
+  ) {
+    if (Serial1.available() > 0) {
+      // read the incoming byte:
+      String readString = Serial1.readStringUntil('\n');
+
+      Serial.print(GLOBAL_IDX);
+      Serial.print(" - ");
+      GLOBAL_IDX++;
+      // say what you got:
+      Serial.print("I received: ");
+      Serial.println(readString);
+      if(SEND_MODE == SendModes::ECHO) {
+        delay(200);
+        Serial.println("Sending back echo message");
+        String sendBack = readString + '\n';
+        Serial1.write(sendBack.c_str());
+      }
+    }
+  }
+  delay(3000);
+}