Fix potential panic in ConstraintTrace display formatting

[anim001k]

Problem

The fmt::Display implementation for ConstraintTrace used metadata.module_path().unwrap(), which could panic if the module path is not available for certain spans (e.g., from macros or external sources).

Solution

Replace unwrap() with unwrap_or(metadata.target()) to provide a safe fallback using the span's target as an alternative identifier.

Changes

• File: relations/src/gr1cs/trace.rs
• Line: 310
• Before: metadata.module_path().unwrap()
• After: metadata.module_path().unwrap_or(metadata.target())