Bundle core inside the integration

HACS and the manual install copy only custom_components/nestquest, so
the integration shipped with a top-level 'core' package that was never
deployed and failed with ModuleNotFoundError: No module named 'core'.

Move core/ into custom_components/nestquest/core/, repoint the
re-export shims to relative '.core.X' imports, and update tests
(import paths, monkeypatch targets, caplog logger) to the new
'custom_components.nestquest.core.X' location. The integration is now
self-contained: nothing under custom_components/nestquest reaches
outside its own tree, the migrations logger becomes
custom_components.nestquest.core.migrations, and the SQL-leak guard
allowlists point at the new core/ paths.

uv run pytest -q: 1496 passed.

tests/test_store.py

@@ -27,7 +27,7 @@ def test_returns_absolute_path_from_config_path(monkeypatch) -> None:
     # Path resolution only: the parent-dir mkdir is a side effect of
     # core.store and is exercised elsewhere; suppress it here so the
     # absolute-path assertion can run against /config (non-writable).
-    monkeypatch.setattr("core.store._ensure_dir", lambda path: None)
+    monkeypatch.setattr("custom_components.nestquest.core.store._ensure_dir", lambda path: None)
     hass = _make_hass(Path("/config"), execute=False)
     db_path = _run(store.async_get_db_path(hass))
     hass.config.path.assert_called_once_with(SQLITE_DB_FILENAME)
@@ -203,7 +203,7 @@ def test_no_file_creation_calls_in_store() -> None:
 
 
 def test_container_style_path_resolves(monkeypatch) -> None:
-    monkeypatch.setattr("core.store._ensure_dir", lambda path: None)
+    monkeypatch.setattr("custom_components.nestquest.core.store._ensure_dir", lambda path: None)
     hass = _make_hass(Path("/config"), execute=False)
     assert _run(store.async_get_db_path(hass)) == Path("/config") / SQLITE_DB_FILENAME