Function def_safety

crates/compile/src/decompile.rs:2009–2011

Map an `is_unsafe` flag to a `DefinitionSafety`. The decompile side uses this to stay in lock-step with `ix::compile::mutual::def_safety`; if we ever want to represent `Partial` explicitly we can refine both sides.

(is_unsafe: bool)

             recursor has {} rules",
            name.pretty(),
            rule_roots.len(),
            rec.rules.len(),
          ),
        });
      }
      (