Fix SPI bugs #9 (NULL platform_ops) and #10 (missing CS toggle), widen chip_select to uint16_t

Bug #9: Both TX and RX SPI init params had platform_ops = NULL, causing
adf4382_init() -> no_os_spi_init() to fail with -EINVAL. Fixed by setting
platform_ops = &stm32_spi_ops and passing stm32_spi_extra with correct CS
port/pin for each device.

Bug #10: stm32_spi_write_and_read() never toggled chip select. Since TX
and RX ADF4382A share SPI4, every register write hit both PLLs. Rewrote
stm32_spi.c to assert CS LOW before transfer and deassert HIGH after,
using stm32_spi_extra metadata. Backward-compatible: legacy callers
(e.g., AD9523) with cs_port=NULL skip CS management.

Also widened chip_select from uint8_t to uint16_t in no_os_spi.h since
STM32 GPIO_PIN_xx values (e.g., GPIO_PIN_14=0x4000) overflow uint8_t.

10/10 tests pass (8 original + 2 new regression tests).

9_Firmware/9_1_Microcontroller/tests/stm32_hal_mock.c

@@ -2,6 +2,7 @@
  * stm32_hal_mock.c -- Spy/recording implementation of STM32 HAL stubs
  ******************************************************************************/
 #include "stm32_hal_mock.h"
+#include "ad_driver_mock.h"
 #include <stdio.h>
 #include <stdlib.h>
 
@@ -262,3 +263,14 @@ void mock_tim_set_compare(TIM_HandleTypeDef *htim, uint32_t Channel, uint32_t Co
         .extra = htim
     });
 }
+
+/* ========================= Mock stm32_spi_ops ===================== */
+
+/* Stub SPI platform ops -- real adf4382a_manager.c references &stm32_spi_ops.
+ * In tests, adf4382_init() is mocked so no_os_spi_init() is never called.
+ * We provide a non-NULL struct so tests can assert platform_ops != NULL. */
+static int mock_spi_init_stub(void) { return 0; }
+
+const struct no_os_spi_platform_ops stm32_spi_ops = {
+    .init = mock_spi_init_stub,
+};