Print variable value on assert failure

Problem to solve

When using a variable as value for a Header assert:

{
echo "GET https://hurl.dev"
echo "HTTP 200"
echo "x-frame-options:Hell{{var1}}"
} | hurl --test --variable "var1=o"

I want to be able to compare what I expect (evaluated value is Hello) and what I get (actual value is SAMEORIGIN), but I only get variable name:

-: Running [1/1]
error: Assert header value
  --> -:3:17
   |
 3 | x-frame-options:Hell{{var1}}
   |                 ^^^^^^^^^^^^ actual value is <SAMEORIGIN>
   |

So to be able to compare values, I have to search for this variable over Hurl file, executed command etc...

Proposal

I think we should print only value or both value and name to make it clearer, for example:

error: Assert header value
  --> -:3:17
   |
 3 | x-frame-options:Hello
   |                 ^^^^^ actual value is <SAMEORIGIN>
   |

error: Assert header value
  --> -:3:17
   |
 3 | x-frame-options:Hell{{var1}} --> Hello
   |                                  ^^^^^ actual value is <SAMEORIGIN>
   |

error: Assert header value
  --> -:3:17
   |
 3 | x-frame-options:Hell{{var1}}
   |                 -----------> Hello
   |                              ^^^^^ actual value is <SAMEORIGIN>
   |

error: Assert header value
  --> -:3:17
   |
 3 | x-frame-options:Hell{{var1}}
   |                 ^^^^^^^^^^^^ expected value is <Hello>
   |                                                 ^^^^^ actual value is <SAMEORIGIN>
   |

error: Assert header value
  --> -:3:17
   |
 3 | x-frame-options:Hello (value of Hell{{var1}})
   |                 ^^^^^ actual value is <SAMEORIGIN>
   |

Reproduce the failure with the Hurl input and the --test --variable command shown in the issue. Trace how the Header assert reports its expected value, then define the chosen display of the evaluated variable and actual response value; done means the failure output makes both values directly comparable.