Replace proof_of_sql_parser::intermediate_ast::UnaryOp with sqlparser::ast::UnaryOp in the proof-of-sql crate

[iajoiner]

Background and Motivation

This issue is a subtask in #235. In short since we plan to add more SQL features we plan to switch to the sqlparser crate which is a feature-rich, no_std-compatible parser used by DataFusion, which is part of the Arrow ecosystem.

Right now we already have some code that can convert intermediate AST from proof-of-sql-parser we use to sqlparser AST. Now we need to systematically replace instances of proof-of-sql-parser constructs with their corresponding sqlparser ones.

Changes Required

• Replace proof_of_sql_parser::intermediate_ast::UnaryOp with sqlparser::ast::UnaryOp in the proof-of-sql crate.
• Make sure no functionality is lost.
• If necessary add error enum variants for unary ops in sqlparser that we don't support yet.

[Abiji-2020]

I would like to work on this issue.

We need to modify the complete unary operator right? or only the expression involving UnaryOp.

[iajoiner]

Closed by #363