Interface Inheritance Cycles are Never Detected

[InsertCreativityHere]

Cycle detection (cycle_detection.rs:19) explicitly covers only structs and enums. Interface inheritance has no cycle check, so slicec/src/grammar/elements/interface.rs:52 recurses forever (the diamond-dedup at line 58 runs after the recursion, so it can't break the loop). Reached during validation via validate_inherited_identifiers → all_inherited_operations(). This is a true infinite recursion, not depth-limited — and the trigger is a plausible typo:

Reproduction

module T
interface I : I {}

Mutual (A : B / B : A) and longer cycles do the same. All exit 127.

Fix

Detect interface-inheritance cycles and report a diagnostic (or add a visited-set to all_base_interfaces).