feat: follow a clone to its parent set

MAME's search path for a set is the set and every ancestor
(src/emu/driver.cpp:31-38, src/emu/romload.cpp:67-84 at mame0289), so
a clone reads the ROMs it shares with its parent from the parent's
archive. games/arcade/<profile>.json now records, under parents, each
parent game set with ROMs and the clones whose romof chain reaches it
before any BIOS set, and rom_search_sets adds them to what a command
reads. The installer's index leaves them out, as it does the sources.

arcade_parent_importer --all is re-run: every profile gains parents,
and mame0258, mame0278, mame2010, mame2015, mame2016 and fbneo also
gain the sources their committed files lacked.

Manifests, EmuDeck and RetroDECK only: videopac.zip reaches
roms/odyssey2 beside i8244.zip, electron.zip roms/electron, and the 35 parent
sets the profile holds (a7800, apple2e, intv, videopac and others)
reach arcade, consolearcade and mame, the folders whose command starts
any machine. verify --all keeps its severity and status counts.

scripts/scraper/arcade_parent_importer.py

@@ -205,6 +205,7 @@ def build_index(
         if n not in bios_names and not e.isdevice and e.runnable and (e.has_roms or e.disks)
     }
     bios: dict[str, set[str]] = {}
+    parents: dict[str, set[str]] = {}
     devices: dict[str, set[str]] = {}
     missing: dict[str, str] = {}
     for name, entry in games.items():
@@ -218,6 +219,12 @@ def build_index(
                 break
             if current in bios_names and parent.has_roms:
                 bios.setdefault(archive(current, current), set()).add(name)
+            elif current not in bios_names and parent.has_roms:
+                # A clone's ROM shared with its parent is looked up in the
+                # parent's archive too: MAME's search path is the set and
+                # every ancestor (src/emu/driver.cpp:31-38,
+                # src/emu/romload.cpp:67-84 at mame0289).
+                parents.setdefault(archive(current, current), set()).add(name)
             current = parent.romof
         for device in set(entry.devices) & device_roms:
             devices.setdefault(device, set()).add(name)
@@ -231,6 +238,7 @@ def build_index(
             sources.setdefault(entry.source, set()).add(archive(name, name))
     return {
         "bios": {k: sorted(v) for k, v in sorted(bios.items())},
+        "parents": {k: sorted(v) for k, v in sorted(parents.items())},
         "devices": {k: sorted(v) for k, v in sorted(devices.items())},
         "chd": sorted(n for n, e in games.items() if e.disks),
         "missing_parents": dict(sorted(missing.items())),