Compiler bug when generating SRAM blocks using a `for` statement

**Describe the bug**
A clear and concise description of what the bug is.

Compiler errors out when trying to run functional simulation for a fairly complex block.

**To Reproduce**
Steps to reproduce the behavior:

- Follow the XLS setup instructions for Ubuntu 2024
- Git clone my [XLS fork](https://github.com/joonho3020/xls/tree/for-loop-issue)
- Run `bazel run -- //xls/modules/snappy:snappy_decomp_test --alsologtostderr --compare=none`

**Expected behavior**
A clear and concise description of what you expected to happen.

Simulation runs. However I get a compile error here : [error source](https://github.com/joonho3020/xls/blob/1ab579996fabd05a39b35818ce71ad2e56b21f8f/xls/modules/snappy/command_executer.x#L103)

If I hand unroll the above loop, I can run simulations without errors, so I'm assuming that this is a frontend compiler bug.

**Screenshots**
If applicable, add screenshots to help explain your problem.

https://github.com/joonho3020/xls/blob/1ab579996fabd05a39b35818ce71ad2e56b21f8f/xls/modules/snappy/command_executer.x#L103

**Environment (this can be helpful for troubleshooting):**
- OS: [e.g. Ubuntu]
- Versions [e.g. 22.04]

**Additional context**
Add any other context about the problem here.