feat: update extractor and transformer constructors to return Extractor interface

internal/app/etl/extractor/mssql.go

@@ -21,7 +21,7 @@ type MssqlExtractor struct {
 	db *sql.DB
 }
 
-func NewMssqlExtractor(db *sql.DB) *MssqlExtractor {
+func NewMssqlExtractor(db *sql.DB) Extractor {
 	return &MssqlExtractor{db: db}
 }
 

internal/app/etl/extractor/postgres.go

@@ -19,7 +19,7 @@ type PostgresExtractor struct {
 	db *pgxpool.Pool
 }
 
-func NewPostgresExtractor(pool *pgxpool.Pool) *PostgresExtractor {
+func NewPostgresExtractor(pool *pgxpool.Pool) Extractor {
 	return &PostgresExtractor{db: pool}
 }
 

internal/app/etl/transformer/mssql.go

@@ -12,7 +12,7 @@ import (
 
 type MssqlTransformer struct{}
 
-func NewMssqlTransformer() *MssqlTransformer {
+func NewMssqlTransformer() Transformer {
 	return &MssqlTransformer{}
 }