nightly-2024-03-09: fix(ssa): Handle mergers of slices returned from calls (#4496)

# Description

## Problem\*

Resolves #4418 

## Summary\*

We need to add handling for slices returned from `ToRadix` and `ToBits`.

~~This PR does two fixes.~~ 
EDIT: After moving to the iterative flattening appraoch w are now
accurately tracking slice capacities when they are the parameters of
blocks.

## Additional Context



## Documentation\*

Check one:
- [ ] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.