fix: Change from COPY to parameterized INSERT for batch inserts

Replace cursor.copy() with cursor.executemany() for more reliable
batch inserts in PostgreSQL. The COPY method has issues with format
and data encoding in psycopg3.

Changes:
- Use executemany() with parameterized INSERT statements
- Let psycopg handle parameter escaping and encoding
- Convert JSONB dicts to JSON strings automatically
- More compatible with various data types

This ensures that data is actually being inserted into PostgreSQL
during migration, fixing the issue where data wasn't appearing in
the database after migration completed.

Fixes: Data not being persisted in PostgreSQL during migration

src/connectors/postgres_connector.py

@@ -101,7 +101,7 @@ class PostgreSQLConnector:
         rows: List[Dict[str, Any]],
         columns: List[str]
     ) -> int:
-        """Insert a batch of rows using COPY (fast bulk insert).
+        """Insert a batch of rows using parameterized INSERT.
 
         Args:
             table: Table name
@@ -116,27 +116,25 @@ class PostgreSQLConnector:
 
         try:
             with self.connection.cursor() as cursor:
-                # Prepare COPY data
-                copy_data = []
+                # Prepare values for INSERT
+                values_list = []
                 for row in rows:
                     values = []
                     for col in columns:
                         val = row.get(col)
-                        if val is None:
-                            values.append("\\N")  # NULL representation
-                        elif isinstance(val, (dict, list)):
+                        # Convert JSONB dicts to JSON strings
+                        if isinstance(val, (dict, list)):
                             values.append(json.dumps(val))
-                        elif isinstance(val, str):
-                            # Escape special characters
-                            val = val.replace("\\", "\\\\").replace("\n", "\\n").replace("\t", "\\t")
-                            values.append(val)
                         else:
-                            values.append(str(val))
-                    copy_data.append("\t".join(values))
+                            values.append(val)
+                    values_list.append(tuple(values))
 
-                # Use COPY for fast insert
-                copy_sql = f"COPY {table} ({','.join(columns)}) FROM STDIN"
-                cursor.copy(copy_sql, "\n".join(copy_data).encode())
+                # Build parameterized INSERT query
+                placeholders = ",".join(["%s"] * len(columns))
+                insert_sql = f"INSERT INTO {table} ({','.join(columns)}) VALUES ({placeholders})"
+
+                # Execute batch insert
+                cursor.executemany(insert_sql, values_list)
                 self.connection.commit()
 
                 logger.debug(f"Inserted {len(rows)} rows into {table}")