Summary

This PR adds STM32C5 HAL v2 USB device support to the shared USBDevice library.

This PR implements the following features:

• HAL v2 USB device low-level adapter for STM32C5
• CDC endpoint and PMA configuration for the C5 USB DRD FS peripheral
• CDC transmit handling compatible with HAL v2 endpoint fields
• Optional CDC line-coding callback for board-specific actions such as 1200-bps touch
• HAL-level USB re-enumeration using HAL_PCD_DeviceDisconnect() and the matching HAL_PCD_Start() attach path

Motivation

The Seeed XIAO STM32C5 uses the STM32C5 HAL v2 USB device peripheral. The shared USBDevice library currently has no HAL v2 low-level adapter, so the board cannot provide USB CDC through the normal Arduino core path.

This change is intentionally separated from the XIAO board definition so the common USB implementation can be reviewed independently. The initial split first used a direct PA_12 GPIO detach in usbd_if.c; after checking the STM32C5 HAL, this was replaced with the HAL PCD device-connect API. The common re-enumeration helper no longer contains a C5-specific pin reference.

Validation

USB CDC enumeration, serial communication and sustained CDC transfers were validated on Seeed XIAO STM32C5. The C5 CDC PMA endpoints are configured as non-overlapping single-buffer areas.

Code formatting

• Ensure AStyle check is passed thanks CI

Closing issues

N/A