Fix test_ecdsa_recover_public_key test

[tcoratger]

Should close #468

The modular inverse should be obtained roughly via the pseudo code:

function inverse(a, n)
    t := 0;     newt := 1
    r := n;     newr := a

    while newr ≠ 0 do
        quotient := r div newr
        (t, newt) := (newt, t − quotient × newt) 
        (r, newr) := (newr, r − quotient × newr)

    if r > 1 then
        return "a is not invertible"
    if t < 0 then
        t := t + n

    return t

In the build_u256_guarantee_inv_mod_n construction, we missed the t < 0 condition, causing this operation https://github.com/starkware-libs/cairo/blob/afeeed29b37bd394535fcf3e8d7d16db047381fb/corelib/src/ecdsa.cairo#L143 to fail in the ECDSA recover_public_key procedure. This issue is fixed and another unit test is added in the u256_inv_mod_n suite to cover this scenario.

Checklist

• Linked to Github Issue
• Unit tests added
• Integration tests added.
• This change requires new documentation.
  • Documentation has been added/updated.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.75%. Comparing base (bd23b1c) to head (e3c669e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #569      +/-   ##
==========================================
+ Coverage   89.74%   89.75%   +0.01%     
==========================================
  Files         108      108              
  Lines       34534    34575      +41     
==========================================
+ Hits        30991    31032      +41     
  Misses       3543     3543              

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[edg-l]

Nice find! Thanks a lot.

[azteca1998]

Nice work, thanks for the fix.