Fix: Don't rewrite_casts for for subclasses like JSONCast

[cory2067]

Description

I noticed a bug in sqlmesh format when working with the ClickHouse dialect. The rewrite_casts option will rewrite exp.JSONCast (the .: operator) to ::, which changes the semantics of the query.

For example,

-- input query
SELECT foo.:String, CAST(bar AS String)

-- expected result
SELECT foo.:String, bar::String

-- observed result
SELECT foo::String, bar::String

This adds a one-line fix by only rewriting exp.Cast itself and not subclasses like exp.JSONCast.

Test Plan

Add unit test for the formatter that makes sure exp.JSONCast is not rewritten, but exp.Cast is still rewritten

Checklist

• I have run make style and fixed any issues
• I have added tests for my changes (if applicable)
• All existing tests pass (make fast-test)
• My commits are signed off (git commit -s) per the DCO