IS-IS: TWAMP Light: Unidirectional link delay advertisement (accelerated and periodic)

This feature enables accelerated and periodic advertisement of TWAMP Light unidirectional link delay measurements in IS-IS. TWAMP Light probe messages measure link performance, and IS-IS traffic engineering extensions distribute the resulting delay information across the network for performance-based path selection. Accelerated advertisement enables rapid notification when measured delay changes exceed a configured threshold, while periodic advertisement reports delay information at configured intervals to provide ongoing visibility without causing unnecessary routing churn.