fix: file mame sets under their systems

934 of the 1,563 mame.yml entries named no system and so served every
system of the profile: each MAME-run system's set was the whole profile.

The 65 BIOS root sets written by hand take the system groovymame.yml
gives the same 0.289 archive (sega-systemsp, konami-gx, taito-gnet and
41 more ids, added to systems:). The 19 XaviX sets take tvgames, the
directory MAME keeps xavix.cpp in. They seed the device walk.

mame_hash_scraper --devices files a device set under arcade when a
machine no entry places loads it: MAME starts such a machine from its
set name, as an arcade folder passes it. 1,106 of the 1,254 device sets
now carry arcade, alone or beside the systems of their placed machines.
qsound, ym2413 and ym2608, written by hand, take the same answer.

Left without a system: 41 device sets no machine of the listxml
instantiates (a software list slot selects them), and the hash/,
plugins/ and floppy/ trees every machine reads.

scripts/scraper/mame_hash_scraper.py

@@ -48,6 +48,7 @@ from .mame_devices import (
     attribute_softlists,
     attribute_systems,
     default_floppy_samples,
+    device_systems,
     drive_form_factor,
     floppy_drives,
     floppy_sample_systems,
@@ -70,6 +71,9 @@ _CLONE_DIR = _ROOT / "tmp" / f"mame-{os.getpid()}"
 _EMULATORS_DIR = _ROOT / "emulators"
 _PLATFORMS_DIR = _ROOT / "platforms"
 _FLOPPY_SOURCE = "src/devices/imagedev/floppy.cpp"
+# Where a device set goes when only machines no seed places load it: MAME
+# starts such a machine from its set name, as an arcade folder passes one.
+UNPLACED_SYSTEM = "arcade"
 _REPO_URL = "https://github.com/mamedev/mame.git"
 _STALE_HOURS = 24
 
@@ -570,9 +574,14 @@ def _merge_devices(args: argparse.Namespace) -> None:
     stated, conflicts = platform_seeds(
         _platform_archives(), machines, profile.get("systems") or [], written
     )
-    systems = attribute_systems(machines, {**stated, **written})
+    seeds = {**stated, **written}
+    systems = attribute_systems(machines, seeds)
+    listed = profile.get("systems") or []
+    filed = device_systems(
+        machines, seeds, UNPLACED_SYSTEM if UNPLACED_SYSTEM in listed else ""
+    )
     for set_name, device in devices.items():
-        device["systems"] = systems.get(set_name, [])
+        device["systems"] = filed.get(set_name, [])
     report = merge_mame_devices(str(profile_path), devices, write=not args.dry_run)
 
     shipped = upstream.list_directory(repo, commit, "hash", upstream.CACHE_DIR)
@@ -602,10 +611,12 @@ def _merge_devices(args: argparse.Namespace) -> None:
     for set_name in report["conflict"]:
         print(f"    ! {set_name}.zip is listed under another category, left as written")
     by_count = Counter(len(device["systems"]) for device in devices.values())
+    fallen = sum(1 for device in devices.values() if UNPLACED_SYSTEM in device["systems"])
     print(
         f"  systems: {by_count[1]} sets under one system, "
         f"{sum(n for k, n in by_count.items() if k > 1)} under several, "
-        f"{by_count[0]} loaded by no placed machine "
+        f"{fallen} of them under {UNPLACED_SYSTEM} (loaded by machines no entry places), "
+        f"{by_count[0]} instantiated by no machine of the release "
         "(they serve every system of the profile)"
     )
     print(