Function init_log_appender 

pub fn init_log_appender() -> Option<SdkLoggerProvider>

Initializes OpenTelemetry log appender if OTEL_EXPORTER_OTLP_ENDPOINT is set.

Returns Some(provider) if initialization succeeds, or None if:

• The env var is unset (noop, zero overhead)
• The exporter fails to build (logs warning, graceful failure)

The provider is returned for use with OpenTelemetryTracingBridge layer.