Make assistant nudge user if they are silent for > n seconds

[katstankiewicz]

• Use EVA_TURN_END_FALLBACK_TIME to set the number of seconds to wait before nudging user
• The assistant will not nudge if user is speaking

todo:

• Small bug fix - if user is speaking or started speaking after the nudge is triggered the assistant doesn't say anything but that turn still gets counted as nudged
• Weird scenario where assistant transcript is not being captured in conversation_trace (the assistant asked if the user was still there after the vad didn't fire on the short turn)

from https://snow-core_llm-eva_results_analysis_plusplus.job.console.elementai.com/record_detail?output_dir=%2Fmnt%2Fvoice_agent%2Fks&record=T6.2&latest_only=false

[raghavm243512]

thanks for catching the bugs