overwrite fix to codehash

[enitrat]

Overwrite fix to codehash done in #1644

Motivation:

I prefer a solution that avoids having invalid states altogether.

• All accounts have a code_hash set to keccak256("") when deployed
• Any modification to the account's code will also modify it's code_hash
• extcodehash simply check the account_exists = has_code_or_nonce or has_balance condition to know whether to return 0 or code_hash

which is more inline with the spec. The codehash of an account is never zero, the extcodehash is.

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 63.9%. Comparing base (71e205d) to head (32d43c4).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cairo_zero/backend/starknet.cairo	0.0%	1 Missing ⚠️
cairo_zero/kakarot/interfaces/interfaces.cairo	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1654     +/-   ##
=======================================
- Coverage   64.2%   63.9%   -0.3%     
=======================================
  Files         44      44             
  Lines       8340    8337      -3     
=======================================
- Hits        5355    5331     -24     
- Misses      2985    3006     +21     

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