fix: record each platform's own list version

install/<platform>.json wrote the constant "1.0" as the version of the
list it was built from. The manifest now carries the version the platform
YAML records, and generate_pack refuses a YAML without one.

inherits: no longer passes a parent's version to a child: Lakka was
published as RetroArch v1.22.2 in its manifest, pack name and site page.
lakka.yml records v6.1, the Lakka-LibreELEC tag its target list is read
at. The MiSTer scraper refuses a BiosDB without a timestamp instead of
writing an empty version.

A pack's manifest.json records list_version, so an install from the pack
alone knows it too. Manifests regenerated twice and compared: only
version and generated changed.

tests/test_install_selection.py

@@ -1021,7 +1021,7 @@ class AHeldFileTheInstallerCannotFetch(unittest.TestCase):
         self.db = {"files": files, "indexes": generate_db.build_indexes(files, {})}
         Path("platforms").mkdir()
         Path("platforms/p.yml").write_text(json.dumps({
-            "platform": "P", "verification_mode": "existence", "cores": ["core"],
+            "platform": "P", "version": "2.1", "verification_mode": "existence", "cores": ["core"],
             "systems": {"sys": {"files": []}},
         }))
         Path("platforms/_registry.yml").write_text(
@@ -1096,7 +1096,7 @@ class AStandaloneLayoutBelowTheBiosFolder(unittest.TestCase):
         self.db = {"files": files, "indexes": generate_db.build_indexes(files, {})}
         Path("platforms").mkdir()
         Path("platforms/p.yml").write_text(json.dumps({
-            "platform": "P", "verification_mode": "existence",
+            "platform": "P", "version": "2.1", "verification_mode": "existence",
             "base_destination": "bios", "cores": ["dsa", "other"],
             "standalone_cores": ["dsa"], "systems": {"sys": {"files": []}},
         }))