perf: Optimize some functions to rewrite dictionary-encoded strings

[andygrove]

What is the problem the feature request solves?

We have some functions that unpack dictionary-encoded strings and then perform a transformation on the unpacked array, but it would be better to transform the dictionary instead. We should optimize these functions to do that.

The functions include:

• hex
• cast string to other types

There may be others.

Describe the potential solution

No response

Additional context

No response

[vaibhawvipul]

I would like to take this up, if no one else is working on it.