Open Policy Agent v1.18.0

This release introduces several quality-of-life improvements for OPA users, specifically around resource management in containerized environments and more detailed policy testing tools. It also includes a breaking change to the outbound User-Agent header to ensure compliance with HTTP standards.

RFC 9110 compliant User-Agent header change — If you use WAF rules, load balancer filters, or log scrapers that verify the 'User-Agent' header for OPA traffic, those checks will fail until updated to expect the new 'Open-Policy-Agent' format. This was necessary to comply with HTTP standards.

Automatic container resource limit detection (GOMEMLIMIT and GOMAXPROCS) — OPA now automatically detects container CPU and memory limits to tune the Go runtime. This prevents 'OOM kills' in memory-constrained environments and ensures optimal thread scaling in Kubernetes without manual environment variable configuration.

Enhanced policy testing and coverage reporting — Policy authors get much better feedback during development through coverage reports that now highlight specific line ranges, rule heads, and complex logical expressions, making it easier to identify untested policy branches.

Correctness fixes for opa fmt and Rego formatting — These fixes ensure that running 'opa fmt' won't accidentally break your Rego code or move comments in a way that changes policy intent, maintaining a clean and safe codebase.