Improve Scope Area and Borrow Checking in Function Definitions and Calls

[notJoon]

1. Function Parameters and Scopes: The previous implementation treated function parameters as uninitialized variables, leading to DeclaredWithoutInitialValue errors. But, for now, I changed check_function_def method to treat function params as initialized variables.

if let Some(args) = args {
   for (arg, is_borrowed) in args {
        self.insert_borrow(arg, BorrowState::Initialized);    // <-

            if *is_borrowed {
               // ...
            }
      }
}

2. Add new scope for each function call and definition :

fn allocate_scope<F, T>(&mut self, action: F) -> T
    where
        F: FnOnce(&mut Self) -> T,
    {
        self.borrows.push(HashMap::new());
        let result = action(self);
        self.borrows.pop();

        result
    }

    fn check_statement(&mut self, stmt: &'a Statement) -> BorrowResult {
        match stmt {
            Statement::VariableDecl {
                name,
                value,
                is_borrowed,
            } => self.check_variable_decl(name, value, *is_borrowed),
            Statement::FunctionDef { name, args, body } => {
                self.allocate_scope(|s| s.check_function_def(name, args, body))
            }
            Statement::Scope(stmts) => self.allocate_scope(|s| s.check(stmts)),
            Statement::Return(expr) => self.check_return(expr),
            Statement::Expr(expr) => self.check_expression(expr),
        }
    }

3. Add more tests

This modifies the check_function_def method to treat function parameters as initialized variables. Additionally, it introduces a new scope for each function call and each function definition, preventing variables from being declared more than once in the same scope.