[DNM]: Stm32c5 halv2 usb rework

[fpistm]

This PR is a review/rework of the stm32duino#3059

• rebase on main branch
• remove useless USBD_V2_ErrorHandler
• remove some useless warning. Ex: #warning "USB device support is currently implemented only for STM32C5xx HAL v2.". Assume by default it should be ok.
• Remove limit CDC transmit blocks to packet size (it will be evaluate against an other PR fix(cdc): stop arming OUT endpoint with a NULL buffer stm32duino/Arduino_Core_STM32#3058).
• Remove add optional hook on CDC line coding change, see feat(usb): add optional hook on CDC line coding change stm32duino/Arduino_Core_STM32#3078. To be evaluate against feat: reboot into the ST system bootloader on a 1200 bps touch stm32duino/Arduino_Core_STM32#3063 which include same behaviour.
• introduce and fix double buffer management.

This PR is functional on Nucleo C562RE (single or double buffer).

/cc @cumin777

[cumin777]

Hi @fpistm, thanks for the rework — reviewed, tested, and force-pushed into stm32duino#3059.

Review

• Generic double-buffer management + the hal_conf/ep_conf macro interlock: cleaner than our C5-specific layout.
• Dropping the transmit clamp and the line-coding hook: agreed. We'll follow feat(usb): add optional hook on CDC line coding change stm32duino/Arduino_Core_STM32#3078 for the XIAO 1200-bps touch handoff; feat(xiao): add Seeed XIAO STM32C5 board support stm32duino/Arduino_Core_STM32#3048 will be rebased once it lands.

On hardware (XIAO STM32C5, same USB_DRD_FS IP as your C562RE)

• Both the default double-buffer and the -DUSBD_CDC_USE_SINGLE_BUFFER builds compiled clean (HAL v2 adapter in artifacts).
• Flashed and enumerated; CDC TX-RX verified: AT round-trips, +READY 170 ms after DTR, 64KB echo loopback with zero bit errors (~267 KB/s).
• Two 5-minute stability runs: 60/60 heartbeats, ~88 MB loopback traffic, no re-enumeration.

Observation on the XIAO (follow-up needed)

• Single write() bursts above ~256 bytes intermittently echo fewer bytes than sent (e.g. 320/512, 640/1024, always a multiple of 64); ≤256 B writes are lossless across 88 MB.
• Present identically in the pre-rework revision of this PR, so not introduced by the rework itself — but both revisions carry the new HAL v2 USB adapter, so I can't yet tell whether it's an adapter-level issue. I'm tracing which direction drops (RX vs TX) and will follow up.

ARM64 and other hosts remain untested on my side, as before.

[fpistm]

Thanks @cumin777

About your issue, could you try with this PR:
stm32duino#3058