gh-131196: Improve perfomance of `UUID.hex` and `UUID.__str__` by ~10% (#131197)

Results before and after the fix:

```
hex
before: 0.021755493999989994
after:  0.01465080400066654 

str
before: 0.06381790500017814
after:  0.05134949700004654
```

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>