drt underflow detected with -DDEBUG_DRT_UNDERFLOW=ON

### Description

After building with `-DDEBUG_DRT_UNDERFLOW=ON`, many drt tests hit an underflow assertion (eg ispd18_test3)

```
[ERROR DRT-0551] subFromByte underflow
```

I think we traced this to patch metal insertion, but I may be wrong.

### Suggested Solution

Completes without any assertions.

### Additional Context

_No response_