Add support for STM32H7S3L8H (H7S3 series)

[jonas-theobald]

Body:

• MCU: STM32H7S3L8H (H7S3 series)
• Board: NUCLEO-H7S3L8
• Requested frameworks: stm32cube (CubeH7) at minimum; Arduino if feasible
• Toolchain: arm-none-eabi-gcc

Details:

• The current framework-stm32cubeh7 package in PlatformIO doesn’t include H7S3 device files or HAL support, so builds cannot target this MCU.
• Please add the device to the ST STM32 platform with a board JSON, upload/debug config (stlink), and ensure the CubeH7 package version includes H7S3 headers/startup/ld scripts.

Thanks!