feat: dataframe-persistent now supports postgres

Also change API to reduce boilerplate.

Author: mchav

.gitignore

@@ -9,6 +9,7 @@ cabal-dev
 *.dyn_o
 *.dyn_hi
 .hpc
+*.tix
 .hsenv
 .cabal-sandbox/
 cabal.sandbox.config
@@ -38,4 +39,10 @@ dataframe-fusion/rust/dfusion-bridge/target
 Cargo.lock
 *.dylib
 *.so
-*.dll
+*.dll
+
+# SQLite sidecar files left by WAL/rollback-journal mode when a .db is opened
+# (transient; the committed *.db fixtures themselves stay tracked).
+*.db-wal
+*.db-shm
+*.db-journal