refactor: import additional Odoo modules and exceptions for expense sheet handling

models/hr_expense_sheet.py

@@ -1,5 +1,7 @@
-from odoo import api, fields, models
+from odoo import api, fields, models, _, Command
 from datetime import timedelta
+from odoo.exceptions import UserError, ValidationError
+from odoo.tools.misc import clean_context
 
 class HrExpenseSheet(models.Model):
     _inherit = 'hr.expense.sheet'