fix: constants for opcodes

[greged93]

Fixes the values of the constants for the opcodes based on the Cairo paper.

[codecov-commenter]

Codecov Report

Merging #318 (ebc719e) into main (e5fcc25) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #318   +/-   ##
=======================================
  Coverage   56.37%   56.37%           
=======================================
  Files          50       50           
  Lines        6634     6634           
=======================================
  Hits         3740     3740           
  Misses       2506     2506           
  Partials      388      388           

Files	Coverage Δ
pkg/vm/instruction.go	97.85% <ø> (ø)

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[fmoletta]

The values of the constants themselves aren't used so this change shouldn't have an impact on the vm's behaviour.
Nevertheless the change does make the code a bit more consistent (given the switch at line 207 )