feat: add UF2 uploader for CDC-touch bootloaders

[cumin777]

Summary

Add uf2upload, a self-contained C++17 host uploader for STM32 boards using
a USB CDC 1200-bps touch and UF2 mass-storage bootloader.

This PR implements the following features:

• Convert a firmware .bin image to UF2 with board-supplied address,
  family ID and maximum-size validation
• Detect an already-mounted UF2 volume, or perform a CDC 1200-bps touch
  and wait for the bootloader volume before copying the UF2 image
• Add Windows and Linux x86_64 tool artifacts

Arduino_Core_STM32 can describe an UF2 upload recipe, but STM32Tools currently
has no uploader that can perform the complete CDC-touch, UF2 conversion and
mass-storage-copy flow. This tool provides that missing user-facing upload
path without requiring Python or shell dependencies at upload time.

On Windows, uf2upload tolerates the transient serial error caused by the
expected reset after the 1200-bps touch and continues waiting for the UF2 volume.

Validation

Validated on a Seeed XIAO STM32C5 running the TinyUF2 bootloader:

• Upload when the XIAOC5BOOT volume is already mounted
• Full automatic flow from a running application: CDC 1200-bps touch,
  bootloader entry, UF2 conversion and copy
• Windows serial-reset status reporting during the device reset transition

The Windows and Linux x86_64 artifacts are included. macOS build integration is
included, but a macOS artifact and hardware validation are not part of this PR.

CI and AStyle checks are pending GitHub Actions.