Use ctx.meta instead of dynamic attribute for database cleanup

Click's Context.meta dictionary is the proper way to store arbitrary
data on the context object, avoiding type checker warnings about
dynamic attribute assignment.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

sqlite_utils/cli.py

@@ -50,20 +50,19 @@ def _register_db_for_cleanup(db):
     ctx = click.get_current_context(silent=True)
     if ctx is None:
         return
-    if not hasattr(ctx, "_databases_to_close"):
-        ctx._databases_to_close = []
+    if "_databases_to_close" not in ctx.meta:
+        ctx.meta["_databases_to_close"] = []
         ctx.call_on_close(lambda: _close_databases(ctx))
-    ctx._databases_to_close.append(db)
+    ctx.meta["_databases_to_close"].append(db)
 
 
 def _close_databases(ctx):
     """Close all databases registered for cleanup."""
-    if hasattr(ctx, "_databases_to_close"):
-        for db in ctx._databases_to_close:
-            try:
-                db.close()
-            except Exception:
-                pass
+    for db in ctx.meta.get("_databases_to_close", []):
+        try:
+            db.close()
+        except Exception:
+            pass
 
 
 VALID_COLUMN_TYPES = ("INTEGER", "TEXT", "FLOAT", "REAL", "BLOB")