fix: always return an array of u8s when simplifying Intrinsic::ToRadix calls

[TomAFrench]

Description

Problem*

Resolves #6662

Summary*

If someone attempts to do a decomposition into radices other than 2 or 256 then we'll end up returning the incorrect type. This PR solves this issue.

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.