Add CAN communication and GPIO control functionality

- Created HAL configuration file for STM32F1xx (stm32f1xx_hal_conf.h).
- Added interrupt handler definitions in stm32f1xx_it.h.
- Implemented CAN initialization and configuration in can.c.
- Configured GPIO pins for output and external interrupts in gpio.c.
- Developed main application logic in main.c for toggling an LED and sending CAN messages.
- Implemented MSP initialization and de-initialization for CAN in stm32f1xx_hal_msp.c.
- Defined interrupt service routines in stm32f1xx_it.c for CAN and EXTI interrupts.
- Added README for project-specific libraries and PlatformIO configuration.
- Created platformio.ini for project build settings.
- Added stm32pio.ini for CubeMX integration with PlatformIO.
- Included README for testing directory to guide unit testing setup.

firmware/components/can_testing/canblinker/Inc/can.h

@@ -0,0 +1,52 @@
+/* USER CODE BEGIN Header */
+/**
+  ******************************************************************************
+  * @file    can.h
+  * @brief   This file contains all the function prototypes for
+  *          the can.c file
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2025 STMicroelectronics.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+/* USER CODE END Header */
+/* Define to prevent recursive inclusion -------------------------------------*/
+#ifndef __CAN_H__
+#define __CAN_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Includes ------------------------------------------------------------------*/
+#include "main.h"
+
+/* USER CODE BEGIN Includes */
+
+/* USER CODE END Includes */
+
+extern CAN_HandleTypeDef hcan;
+
+/* USER CODE BEGIN Private defines */
+
+/* USER CODE END Private defines */
+
+void MX_CAN_Init(void);
+
+/* USER CODE BEGIN Prototypes */
+
+/* USER CODE END Prototypes */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __CAN_H__ */
+