Add expected value field in all assert Error Message

Currently, the expected value is taken from the input Hurl file
for example

error: Assert body value
  --> tests_failed/assert_base64.hurl:12:8
   |
   | GET http://localhost:8000/error-assert-base64
   | ...
12 | base64,bGluZTEKbGluZTIKbGluZTMK;
   |        ^^^^^^^^^^^^^^^^^^^^^^^^ actual value is <hex, 6c696e65310a6c696e65320d0a6c696e65330a;>
   |

Display the expected value along the actual value using the same format.

error: Assert body value
  --> tests_failed/assert_base64.hurl:12:8
   |
   | GET http://localhost:8000/error-assert-base64
   | ...
12 | base64,bGluZTEKbGluZTIKbGluZTMK;
   |        ^^^^^^^^^^^^^^^^^^^^^^^^ expected: <hex, 6c696e65310a6c696e65320d0a6c696e65330a;>
   |                                 actual:   <hex, 6c696e65310a6c696e65320d0a00696e6533;>
   |