refactor: make Query module pure

This splits off the transaction concerns into a MainTx module

It's just moving some functions inside the Query module to the MainTx module.
Some types names were also changed so they don't have the "Query" prefix, to avoid confusion.

src/PostgREST/App.hs

@@ -35,6 +35,7 @@ import qualified PostgREST.Cors       as Cors
 import qualified PostgREST.Error      as Error
 import qualified PostgREST.Listener   as Listener
 import qualified PostgREST.Logger     as Logger
+import qualified PostgREST.MainTx     as MainTx
 import qualified PostgREST.Plan       as Plan
 import qualified PostgREST.Query      as Query
 import qualified PostgREST.Response   as Response
@@ -143,14 +144,14 @@ postgrestResponse appState conf@AppConfig{..} maybeSchemaCache authResult@AuthRe
   (planTime, plan)                   <- withTiming $ liftEither $ Plan.actionPlan iAction conf apiReq sCache
 
   let mainQ = Query.mainQuery plan conf apiReq authResult configDbPreRequest
-      query = Query.mainTx mainQ conf authResult apiReq plan sCache
+      tx = MainTx.mainTx mainQ conf authResult apiReq plan sCache
       observer = AppState.getObserver appState
       obsQuery s = when (configLogQuery /= LogQueryDisabled) $ observer $ QueryObs mainQ s
 
-  (queryTime, queryResult) <- withTiming $ do
-    case query of
-      Query.NoDbQuery r -> pure r
-      Query.DbQuery{..} -> do
+  (txTime, txResult) <- withTiming $ do
+    case tx of
+      MainTx.NoDbTx r -> pure r
+      MainTx.DbTx{..} -> do
         dbRes <- lift $ AppState.usePool appState (dqTransaction dqIsoLevel dqTxMode $ runExceptT dqDbHandler)
         let eitherResp = join $ mapLeft (Error.PgErr . Error.PgError (Just authRole /= configDbAnonRole)) dbRes
 
@@ -161,14 +162,14 @@ postgrestResponse appState conf@AppConfig{..} maybeSchemaCache authResult@AuthRe
         liftEither eitherResp
 
   (respTime, resp) <- withTiming $ do
-    let response = Response.actionResponse queryResult apiReq (T.decodeUtf8 prettyVersion, docsVersion) conf sCache iSchema iNegotiatedByProfile
+    let response = Response.actionResponse txResult apiReq (T.decodeUtf8 prettyVersion, docsVersion) conf sCache iSchema iNegotiatedByProfile
         status' = either Error.status Response.pgrstStatus response
 
     -- TODO: see above obsQuery, only this obsQuery should remain after refactoring (because the QueryObs depends on the status)
     lift $ obsQuery status'
     liftEither response
 
-  return $ toWaiResponse (ServerTiming jwtTime parseTime planTime queryTime respTime) resp
+  return $ toWaiResponse (ServerTiming jwtTime parseTime planTime txTime respTime) resp
 
   where
     toWaiResponse :: ServerTiming -> Response.PgrstResponse -> Wai.Response