[dv/formal]: With Yosys and rIC3 fails for python conductor.py prove.

Nobody has claimed this yet.

## Observed Behavior
I tried to re-run the dv/formal flow using the Opensource tools using the following instructions:
**Build instructions:**

- nix develop .#oss-dev
- make build/aig-manip builds the Rust aig-manip tool used by conductor.py
- make build/all.aig builds the core Aiger file
- python3 conductor.py prove

but the run crashed with Error code 127. I attached the log file also for the crash.

## Expected Behavior
In the link here https://semiiphub.com/industryexpertblogs/open-source-correctness-proof-for-ibex it was mentioned that dv/formal is part of the latest CI. Thus I was hoping it must pass.

## Steps to reproduce the issue
Commands I ran:
- git clone https://github.com/lowRISC/ibex.git
- cd dv/formal
- nix develop .#oss-dev
- make build/aig-manip builds the Rust aig-manip tool used by conductor.py
- make build/all.aig builds the core Aiger file
- python3 conductor.py

At pyhon3 conductor.py prove got lot of errors with Error code 127,

## My Environment

[log_file.txt](https://github.com/user-attachments/files/25871318/log_file.txt)

**Operating system:**
Distributor ID: Ubuntu
Description: Ubuntu 24.04.4 LTS
Release: 24.04

**Version of the Ibex source code:**
branch: master

Start in dv/formal/conductor.py and reproduce the failure with nix develop .#oss-dev, make build/aig-manip, make build/all.aig, and python3 conductor.py prove. Inspect the attached log for the command producing Error 127; done means the documented open-source formal flow completes successfully on the reported environment.

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