fix: Update AsanPardakht gateway implementation

- Resolved issue with missing 'username' attribute in AsanPardakht class by ensuring proper variable assignment.
- Modified the  method to correctly set , , and  attributes.
- Implemented proper error handling in  method for better handling of HTTP errors and exceptions.
- Refactored the  method to retrieve server time from Asan Pardakht API.
- Enhanced logging to provide better debug information during payment process and error scenarios.

Related to issue ali-zahedi#119

README.md

@@ -31,6 +31,8 @@
 
  1. [درگاه پی ورژن ۱](https://www.pay.ir/)
 
+ 1. [درگاه آسان پرداخت ](https://www.asanpardakht.ir/)
+
 [[_TOC_]]
 
 <h1 dir="rtl">آموزشی</h1>
@@ -96,6 +98,11 @@
              "MERCHANT_CODE": "<YOUR MERCHANT CODE>",
              "X_SANDBOX": 0,  # 0 disable, 1 active
          },
+       "ASANPARDAKHT": { 
+           "MERCHANT_CONFIGURATION_ID": "<YOUR MERCHANT CONFIGURATION ID>",
+           "USERNAME": "<YOUR USERNAME>",
+           "PASSWORD": "<YOUR PASSWORD>",
+       },
      },
      "IS_SAMPLE_FORM_ENABLE": True,  # اختیاری و پیش فرض غیر فعال است
      "DEFAULT": "BMI",