fix: Lazily elaborate functions in comptime interpreter

[jfecher]

Description

Problem*

Resolves #5538 (comment)

Summary*

If a function with an empty body is found within the comptime interpreter we now lazily elaborate it instead of failing with an error.

Additional Context

The test for this is noir_test_success_comptime_globals which after #5538 requires lazy elaboration due to comptime globals themselves now being elaborated before functions.

This PR opens the way to be more lax about marking functions comptime and potentially lets us remove the restriction that you can only call non-comptime functions in separate modules.

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.

[michaeljklein]

Small question r.e. tearing down the fresh elaborator, otherwise LGTM