Add disk-backed SQLite cache mode as an alternative to in-memory

src/sqlmem/engine.py

@@ -8,7 +8,12 @@ from sqlalchemy import inspect
 from sqlalchemy.engine import Engine
 
 from .cache import CacheManager
-from .config import BACKUP_INTERVAL_SECONDS, CACHE_DB_PATH, REFRESH_INTERVAL_SECONDS
+from .config import (
+    BACKUP_INTERVAL_SECONDS,
+    CACHE_DB_PATH,
+    IN_MEMORY,
+    REFRESH_INTERVAL_SECONDS,
+)
 from .delta import DeltaConfig, DeltaRefresher, ResolvedDelta
 from .executor import QueryExecutor
 from .parser import Params, parse
@@ -25,9 +30,13 @@ class CachingEngine:
         delta: dict[str, DeltaConfig] | None = None,
         ttl: dict[str, int] | None = None,
         indexes: dict[str, list[str | list[str]]] | None = None,
+        in_memory: bool | None = None,
     ) -> None:
         self._source_engine = source_engine
-        self._cache = CacheManager(CACHE_DB_PATH, BACKUP_INTERVAL_SECONDS)
+        use_memory = IN_MEMORY if in_memory is None else in_memory
+        self._cache = CacheManager(
+            CACHE_DB_PATH, BACKUP_INTERVAL_SECONDS, in_memory=use_memory
+        )
         self._registry = ColumnRegistry(self._cache.connection)
         self._stats = StatsCollector()
         self._refresh_interval = REFRESH_INTERVAL_SECONDS