Add three new gems for UART serial communication:
- hw-uart: common Ruby API, C bindings, ring buffer, and HAL header
- hw-esp32-uart: ESP32 HAL using ESP-IDF UART driver with FreeRTOS
RX task
- hw-rp2040-uart: RP2040 HAL using Pico SDK with IRQ-driven RX
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto