feat: Implement Char from FieldElement

[phated]

Description

Problem*

Resolves

Summary*

While working on noir-lang/noir#2373, I noticed that we have code that converts a FieldElement into a char so we can collect them into a String. This adds a proper From implementation so we don't need the custom code like https://github.com/noir-lang/noir/blob/master/crates/noirc_abi/src/lib.rs#L394-L399

Additional Context

PR Checklist*

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

[TomAFrench]

Do we want to turn the assert into an error and have this be a TryFrom? (The unwrap can be left as is as it should never trigger).

[phated]

Do we want to turn the assert into an error and have this be a TryFrom? (The unwrap can be left as is as it should never trigger).

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