feat(sol): add CastExpr to solidity

[iajoiner]

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Rationale for this change

We need to allow casting in the Solidity verifier.

What changes are included in this PR?

See title.

Are these changes tested?

Yes.

[codecov]

Codecov Report

Attention: Patch coverage is 98.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.09%. Comparing base (a8e21f9) to head (2e0524f).

Files with missing lines	Patch %	Lines
...rates/proof-of-sql/src/sql/evm_proof_plan/exprs.rs	98.80%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #751   +/-   ##
=======================================
  Coverage   96.08%   96.09%           
=======================================
  Files         331      331           
  Lines       58897    58987   +90     
=======================================
+ Hits        56593    56682   +89     
- Misses       2304     2305    +1     

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