Open Policy Agent v1.18.1

This is a targeted bug fix release addressing a significant memory leak introduced in v1.17.0 related to the Abstract Syntax Tree (AST) annotations. It resolves issues where the OPA server process would consume excessive memory over time.

Resolved critical memory leak in AnnotationSet — Users running OPA in server mode may have experienced steadily increasing memory consumption since v1.17.0, which could eventually lead to OOM (Out Of Memory) kills and service instability. This fix restores operational reliability and predictable resource usage.