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/main.h

@@ -0,0 +1,69 @@
+/* USER CODE BEGIN Header */
+/**
+  ******************************************************************************
+  * @file           : main.h
+  * @brief          : Header for main.c file.
+  *                   This file contains the common defines of the application.
+  ******************************************************************************
+  * @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 __MAIN_H
+#define __MAIN_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Includes ------------------------------------------------------------------*/
+#include "stm32f1xx_hal.h"
+
+/* Private includes ----------------------------------------------------------*/
+/* USER CODE BEGIN Includes */
+
+/* USER CODE END Includes */
+
+/* Exported types ------------------------------------------------------------*/
+/* USER CODE BEGIN ET */
+
+/* USER CODE END ET */
+
+/* Exported constants --------------------------------------------------------*/
+/* USER CODE BEGIN EC */
+
+/* USER CODE END EC */
+
+/* Exported macro ------------------------------------------------------------*/
+/* USER CODE BEGIN EM */
+
+/* USER CODE END EM */
+
+/* Exported functions prototypes ---------------------------------------------*/
+void Error_Handler(void);
+
+/* USER CODE BEGIN EFP */
+
+/* USER CODE END EFP */
+
+/* Private defines -----------------------------------------------------------*/
+
+/* USER CODE BEGIN Private defines */
+
+/* USER CODE END Private defines */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __MAIN_H */