Fix CairoRunner::write_output so that it prints missing and relocatable values

[fmoletta]

Currently our vm only prints values in the output segment if they are integer values, and fails if they are not.
This PR aims to fix this behaviour and also print missing and relocatable values as the original vm does.
Expample program:

%builtins output

func main{output_ptr: felt*}() {
    //Memory Gap + Relocatable value
    assert [output_ptr + 1] = cast(output_ptr, felt);
    let output_ptr = output_ptr + 2;
    return ();
}

Example program output:

Program Output: 
<missing>
2:0

Depends on #852

[codecov]

Codecov Report

Merging #853 (ee0b2c8) into memory-get-option (2016148) will decrease coverage by 0.01%.
The diff coverage is 97.56%.

@@                  Coverage Diff                  @@
##           memory-get-option     #853      +/-   ##
=====================================================
- Coverage              96.78%   96.78%   -0.01%     
=====================================================
  Files                     69       69              
  Lines                  28726    28757      +31     
=====================================================
+ Hits                   27802    27832      +30     
- Misses                   924      925       +1     

Impacted Files	Coverage Δ
src/vm/runners/cairo_runner.rs	97.53% <97.56%> (-0.01%)	⬇️

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[Oppen]

For a later refactor: it could be a better idea to implement Display for Felt instead.

[fmoletta]

It is implemented, the reason for using to_bigint() is to change the range of the felt (from [0,P] to [-P/2, P/2})