[minor] more readable generated nim wrappers
from https://ptpb.pw/-vx0/nim

```nim
proc svDpiVersion*(): cstring {.importc: "svDpiVersion", header: headersvdpi.}
proc svGetBitselBit*(s: ptr svBitVecVal; i: cint): svBit {.importc: "svGetBitselBit",
    header: headersvdpi.}
...
```

=>

```nim
{.push header: "headersvdpi".}
proc svDpiVersion*(): cstring {.importc: "$1".}
proc svGetBitselBit*(s: ptr svBitVecVal; i: cint): svBit {.importc: "$1".}
...
{.pop.}
```
