fix: count a missing core file once in the summary

The closing summary of verify --all grouped platform to names: sfiii2a.zip,
missing on 15 platforms, was printed 15 times on a 1 060-character line and
counted 24 files for 10 distinct ones. It now groups by file and names the
platforms by the shorter side (every platform but BizHawk, MinUI, MiSTer
FPGA).

scripts/verify.py

@@ -3121,6 +3121,13 @@ def _overall_summary(group_results: list[tuple[dict, list[str]]]) -> str:
         named = [f"{name} {count}" for name, count in counts.items() if count]
         return f" ({', '.join(named)})" if named else ""
 
+    def on(groups: tuple[str, ...]) -> str:
+        """The platforms a file is missing on, by the shorter side."""
+        if len(group_results) < 2 or len(groups) * 2 <= len(group_results):
+            return ", ".join(groups)
+        others = [" / ".join(g) for _, g in group_results if " / ".join(g) not in groups]
+        return "every platform" + (f" but {', '.join(others)}" if others else "")
+
     parts = []
     for severity, label in ((Severity.CRITICAL, "critical"), (Severity.WARNING, "warning"),
                             (Severity.INFO, "info")):
@@ -3139,18 +3146,26 @@ def _overall_summary(group_results: list[tuple[dict, list[str]]]) -> str:
     parts.append(f"{total} {'discrepancy' if total == 1 else 'discrepancies'}{where(counts)}")
     lines = [f"{platforms} platforms: {', '.join(parts)}"]
 
-    missing = {
-        " / ".join(group): sorted({
+    # Grouped by file, not by platform: sfiii2a.zip missing everywhere was
+    # counted and printed once per platform, 24 files for 10 distinct ones.
+    holders: dict[str, list[str]] = {}
+    for r, group in group_results:
+        for name in sorted({
             u["name"] for u in _core_required_missing(_split_undeclared(
                 r.get("undeclared_files", []))[1])
-        })
-        for r, group in group_results
-    }
-    total = sum(len(names) for names in missing.values())
-    if total:
-        detail = "; ".join(f"{group}: {', '.join(names)}"
-                           for group, names in missing.items() if names)
-        lines.append(f"{total} core file(s) a core cannot run without are missing ({detail})")
+        }):
+            holders.setdefault(name, []).append(" / ".join(group))
+    if holders:
+        by_platforms: dict[tuple[str, ...], list[str]] = {}
+        for name, groups in sorted(holders.items()):
+            by_platforms.setdefault(tuple(groups), []).append(name)
+        detail = "; ".join(
+            f"{', '.join(names)} ({on(groups)})"
+            for groups, names in sorted(by_platforms.items(),
+                                        key=lambda item: (-len(item[0]), item[1]))
+        )
+        lines.append(f"{len(holders)} core file(s) a core cannot run without are "
+                     f"missing: {detail}")
     for category, label in _NOT_FIRMWARE.items():
         counts = {
             " / ".join(group): len((r.get("missing_not_firmware") or {}).get(category, []))