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/stm32f1xx_it.h

@@ -0,0 +1,68 @@
+/* USER CODE BEGIN Header */
+/**
+  ******************************************************************************
+  * @file    stm32f1xx_it.h
+  * @brief   This file contains the headers of the interrupt handlers.
+  ******************************************************************************
+  * @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 __STM32F1xx_IT_H
+#define __STM32F1xx_IT_H
+
+#ifdef __cplusplus
+ extern "C" {
+#endif
+
+/* 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 NMI_Handler(void);
+void HardFault_Handler(void);
+void MemManage_Handler(void);
+void BusFault_Handler(void);
+void UsageFault_Handler(void);
+void SVC_Handler(void);
+void DebugMon_Handler(void);
+void PendSV_Handler(void);
+void SysTick_Handler(void);
+void CAN1_RX1_IRQHandler(void);
+void EXTI9_5_IRQHandler(void);
+/* USER CODE BEGIN EFP */
+
+/* USER CODE END EFP */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __STM32F1xx_IT_H */