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_frontend_digest.py

@@ -47,6 +47,7 @@ class FrontendDigestDecides(unittest.TestCase):
         )
         (self.platforms / "digestplat.yml").write_text(yaml.safe_dump({
             "platform": "DigestPlat",
+            "version": "2.1",
             "verification_mode": "md5",
             "base_destination": "bios",
             "systems": {"psx": {"files": [{