Codegen cannot handle negative steps in maps

**Description**
I think there are actually two separate bugs here, but they are related.
1. Codegen produces wrong code for negative steps in maps with sequential schedule.
2. Codegen produces wrong code for symbolic steps, which are negative at runtime with default schedule.

**To Reproduce**
[reproduce.py](https://github.com/user-attachments/files/26718256/reproduce.py)

**Expected behavior**
All testcases above should pass

**Desktop (please complete the following information):**
- OS: Ubuntu 24.04.3 LTS