feat: implement Postgres loader and refactor migration job processing

cmd/go_migrate/process.go

@@ -10,6 +10,7 @@ import (
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/custom_errors"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl/extractor"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl/loader"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl/transformer"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
 	"github.com/jackc/pgx/v5/pgxpool"
@@ -63,6 +64,7 @@ func processMigrationJob(
 
 	mssqlExtractor := extractor.NewMssqlExtractor(sourceDb)
 	mssqlToPostgresTransformer := transformer.NewMssqlTransformer()
+	postgresLoader := loader.NewPostgresLoader(targetDb)
 
 	go func() {
 		if err := custom_errors.JobErrorHandler(jobCtx, chJobErrors); err != nil {
@@ -120,7 +122,16 @@ func processMigrationJob(
 
 	for range job.MaxLoaders {
 		wgLoaders.Go(func() {
-			loadRowsPostgres(jobCtx, targetDb, job.TargetTable, targetColTypes, chChunksTransformed, chLoadersErrors, chJobErrors, &wgActiveChunks, &rowsLoaded)
+			postgresLoader.Exec(
+				jobCtx,
+				job.TargetTable,
+				targetColTypes,
+				chChunksTransformed,
+				chLoadersErrors,
+				chJobErrors,
+				&wgActiveChunks,
+				&rowsLoaded,
+			)
 		})
 	}