fix: generate program_json directly from program string

[MegaRedHand]

Closes #757

Description

Class hashes were calculated incorrectly when using the TryFrom<BufReader<T>> implementation. This was because we were deserializing the string into a starknet_api::ContractClass and later serializing that again. This PR fixes this by reading everything into a string, and later using the TryFrom<&str> implementation.

NOTE: due to the class hash change some proxy tests were broken (and had to be fixed)

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

Merging #764 (fa6fd36) into main (66a978b) will increase coverage by 0.03%.
The diff coverage is 97.67%.

@@            Coverage Diff             @@
##             main     #764      +/-   ##
==========================================
+ Coverage   92.42%   92.45%   +0.03%     
==========================================
  Files          51       51              
  Lines       11847    11945      +98     
==========================================
+ Hits        10949    11044      +95     
- Misses        898      901       +3     

Impacted Files	Coverage Δ
.../api/contract_classes/deprecated_contract_class.rs	96.88% <97.61%> (+0.03%)	⬆️
crates/starknet-contract-class/src/lib.rs	79.56% <100.00%> (ø)