docs: homogenize doxygen comments across core, libraries and variants

Review doxygen comments in headers and sources under cores/, libraries/,
system/STM32* and variants/ (excluding cores/arduino/api, system/Drivers
and system/Middlewares) and apply one style:

- API contracts (@brief, @PARAM, @return, @note) live in headers. Functions
  declared in a header are documented there and their duplicate blocks are
  removed from the source file.
- Static and source-only functions are documented directly above their
  definition in the .c/.cpp file.
- Parameter names in header declarations now match their definitions in
  HardwareTimer.h, analog.h, Wire.h, and VirtIO mbox_ipcc.h. This is a
  name-only change with no ABI impact.
- @RetVal None on void functions is replaced by @return or dropped. Remaining
  @RetVal tags are kept only in ST-derived HAL/LL, system and middleware files.
- Undocumented functions are documented, including HardwareTimer methods,
  Wire and twi helpers, SPI, EEPROM, Servo, USBDevice, Serial Uart, WSerial
  serialEvent hooks, pins_arduino, variant clock helpers, and assert_failed in
  the hal_conf_default headers.

Function-level 'not documented' doxygen warnings drop from 197 to 2. In
USBDevice, the #ifdef blocks in usbd_cdc.h and usbd_hid_composite.h are
reordered with equivalent declarations. Comment-stripped code is otherwise
unchanged.

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>
Assisted-by: GitHub Copilot: Claude Haiku 5.5

Author: fpistm

CI/update/templates/generic_clock.c

@@ -15,9 +15,7 @@
 #include "pins_arduino.h"
 
 /**
-  * @brief  System Clock Configuration
-  * @param  None
-  * @retval None
+  * @brief System Clock Configuration
   */
 WEAK void SystemClock_Config(void)
 {