Function setup_from_env 

pub fn setup_from_env()

Initialize tracing from standard OpenTelemetry environment variables:

• OTEL_SERVICE_NAME — service name (default "rws")
• OTEL_EXPORTER_OTLP_TRACES_ENDPOINT — full traces URL, used as is; else OTEL_EXPORTER_OTLP_ENDPOINT (the collector’s base URL, /v1/traces appended); neither set → stdout
• OTEL_EXPORTER_OTLP_HEADERS — key=value,… sent with every export (OTEL_EXPORTER_OTLP_TRACES_HEADERS wins)
• OTEL_TRACES_SAMPLER_ARG — sample rate 0.0–1.0 (default 1.0)

Metrics export is separate: metrics::start_from_env.