core/sqlite: extract immutable connection helper

use in bluemaestro/zotero modules

my/core/sqlite.py

@@ -0,0 +1,25 @@
+from .common import assert_subpackage; assert_subpackage(__name__)
+
+import sqlite3
+
+from .common import PathIsh
+
+def sqlite_connect_immutable(db: PathIsh) -> sqlite3.Connection:
+    # https://www.sqlite.org/draft/uri.html#uriimmutable
+    return sqlite3.connect(f'file:{db}?immutable=1', uri=True)
+
+
+from pathlib import Path
+def test_sqlite_connect_immutable(tmp_path: Path) -> None:
+    db = str(tmp_path / 'db.sqlite')
+    with sqlite3.connect(db) as conn:
+        conn.execute('CREATE TABLE testtable (col)')
+
+    import pytest  # type: ignore
+    with pytest.raises(sqlite3.OperationalError, match='readonly database'):
+        with sqlite_connect_immutable(db) as conn:
+            conn.execute('DROP TABLE testtable')
+
+    # succeeds without immutable
+    with sqlite3.connect(db) as conn:
+        conn.execute('DROP TABLE testtable')