fix: revert breaking change on public input serialization

[odesenfans]

Context: integration of the OS + bootloader with the Stone prover.

Problem: The 0x prefix was removed from public memory hex values in fe72ee0. This is incompatible with the Stone prover and causes the following exception:

terminate called after throwing an instance of 'starkware::StarkwareException'
what():  /app/src/starkware/utils/to_from_string.cc:60: String ("40780017fff7fff") does not start with '0x'.

Solution: revert the change + fix the serialization/deserialization test.

Checklist

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.79%. Comparing base (5d11811) to head (fdf3fee).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1790   +/-   ##
=======================================
  Coverage   94.79%   94.79%           
=======================================
  Files         102      102           
  Lines       40141    40142    +1     
=======================================
+ Hits        38050    38051    +1     
  Misses       2091     2091           

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[fmoletta]

This is currently working fine, the public memory values are being serialized as hex values prefixed by "0x" in the air public input file output. You can also see that introducing this change makes comparisons against the python vm fail in the CI

[pefontana]

Hi @odesenfans !
Can yoy solve some merge conflicts here so we can merge it!
The Serialization part we already added here #1799