Publish continuous ESAD state telemetry

[ryanjAA]

Summary

• Publish HEARTBEAT and current ESAD_STATE at 1 Hz
• Preserve immediate ESAD_STATE responses after ARM and SAFE requests
• Update the direct host test to ignore buffered periodic state messages
• Use the supported STM32 Uart implementation for the NUCLEO-F103RB link
• Document continuous state reporting and the verified memory footprint

Validation

• NUCLEO-F103RB firmware compiled successfully with STM32 Arduino core 3.0.0
• Firmware uses 15 percent flash and 10 percent RAM
• Python host tools passed bytecode compilation
• Firmware flashed successfully to a connected NUCLEO-F103RB
• AAGS (our QGC) continuously displayed fresh ESAD Safe telemetry beyond its five second freshness threshold