Remove dynamic memory allocation (malloc/calloc/free)

- Add static memory pool implementation (se050_mem_pool.c/h)
- Replace all malloc/calloc with pool allocations
- Replace all free with pool deallocations
- Remove strdup usage (use fixed-size buffer instead)
- Update I2C HAL to use fixed-size dev_path array
- All 24 tests pass with static memory only

Suitable for embedded environments (u-boot, ESP32) without heap.

include/se050_i2c_hal.h

@@ -7,6 +7,8 @@
 #define SE050_I2C_HAL_H
 
 #include <stdint.h>
+#include <stddef.h>
+#include <string.h>
 
 /* Status codes */
 typedef enum {
@@ -24,10 +26,12 @@ typedef enum {
 } se050_status_t;
 
 /* I2C HAL structure */
+#define SE050_I2C_DEV_PATH_MAX  64
+
 typedef struct {
     void *handle;           /**< I2C file descriptor */
     uint8_t slave_addr;     /**< I2C slave address */
-    const char *dev_path;   /**< I2C device path */
+    char dev_path[SE050_I2C_DEV_PATH_MAX];  /**< I2C device path */
     int wakeup_pin;         /**< Wakeup GPIO pin (-1 if unused) */
 } se050_i2c_hal_t;