Fix OpenDisplay config-entry persistence after device deletion

[Copilot]

Home Assistant could not persist OpenDisplay config-entry changes because the integration stored raw bytes in entry data. When storage writes failed, deleting the device/integration entry did not survive restart and the same device reappeared in initialize state.

• Config-entry migration on setup

  • Normalize legacy entry data before Home Assistant writes it back.
  • Convert stored encryption keys from raw bytes to lowercase hex strings.
  • Drop cached runtime config blobs if they still contain byte fields and cannot be safely persisted.

• JSON-safe cached device config

  • Replace ad-hoc dataclass serialization with the library’s config JSON serializer.
  • Deserialize cached config through the matching library parser so deep-sleep recovery still works without reintroducing non-serializable fields.

• Legacy auth-key compatibility

  • Keep service-side key handling tolerant of older byte-backed entries during the transition window, so existing installs can self-heal on next startup.

• Regression coverage

  • Add coverage for legacy byte-backed entry data and for JSON-safe cache writes.

Example of the migration behavior:

normalized = _normalize_entry_data(
    {
        CONF_ENCRYPTION_KEY: b"\x01" * 16,
        CONF_CACHED_DEVICE_CONFIG: {"system": {"reserved": b"\x00" * 15}},
        CONF_CACHED_FIRMWARE: {"major": 1, "minor": 0},
        CONF_CACHED_IS_FLEX: False,
    }
)

# persisted safely
assert normalized[CONF_ENCRYPTION_KEY] == "01" * 16
assert CONF_CACHED_DEVICE_CONFIG not in normalized

[Misiu]

@copilot ok, were in devcontainers, you can run tests

[Copilot]

@copilot ok, were in devcontainers, you can run tests

I ran the local validation path in the repo. scripts/setup succeeds, but python -m pytest -q tests/test_deep_sleep_runtime_sync.py is currently blocked during collection by an unrelated Home Assistant selector compatibility issue in custom_components/opendisplay/services.py (MediaSelectorConfig(accept=["image/*"]) is rejected by the installed HA version with extra keys not allowed @ data['accept']). I didn’t make code changes for this PR because that failure is outside the config-entry persistence fix.