Extremely inefficient `hash` implementation for `cstring`
### Description

https://github.com/nim-lang/Nim/blob/dcc4e07e546e515a04767d31c3fdd0342cc7ed86/lib/pure/hashes.nim#L570 - the implementation calls itself efficient, but the first thing it does is allocate a copy of the `cstring`.

### Nim Version

devel, earlier

### Current Output

_No response_

### Expected Output

_No response_

### Known Workarounds

_No response_

### Additional Information

_No response_