Report fences validated, not fences attempted

`total` counts every fence the gate ATTEMPTS, and the summary printed it
as "validated". With nothing failing the two coincide, which is why it
went unnoticed — every green run reported honestly. But a run with
failures overstated its own success: a sample measurement here printed
"19 fence(s) validated, 0 skipped, 10 failed", where only 9 passed.

Now prints passes, with the attempted count alongside so the arithmetic
still reconciles.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: reid-spencer

scripts/validate-riddl-examples.py

@@ -421,7 +421,12 @@ def main() -> int:
                 for ln in detail.split("\n")[:8]:
                     print("    " + ln)
 
-    print(f"\n{total} fence(s) validated, {skipped} skipped, {failed} failed")
+    # `total` counts fences ATTEMPTED, so the passing count is total - failed.
+    # Reporting `total` as "validated" overstates it whenever anything failed.
+    print(
+        f"\n{total - failed} fence(s) validated, {skipped} skipped, "
+        f"{failed} failed ({total} attempted)"
+    )
     return 1 if failed else 0