fix(test): break on unknown signal in count_concat_bits

When an unknown signal is encountered, total is set to -1 but the
loop continues. Subsequent known signals add their widths to -1,
producing incorrect totals (e.g. -1 + 16 = 15 instead of -1).
This can mask genuine truncation bugs in status word packing.

9_Firmware/tests/cross_layer/contract_parser.py

@@ -497,6 +497,7 @@ def count_concat_bits(concat_expr: str, port_widths: dict[str, int]) -> ConcatWi
             # Unknown width — flag it
             fragments.append((part, -1))
             total = -1  # Can't compute
+            break
 
     return ConcatWidth(
         total_bits=total,