feat: date does not support dots, gnu does in 9.11

Hi, uutils mainteners

it seems uu date

```rust
relunsec@relunsec:~/software/coreutils/target/debug$ ./date -d "11.12.2026"
date: invalid date '11.12.2026'
relunsec@relunsec:~/software/coreutils/target/debug$ 
```

not support at all that gnu coreutils 9.11 feature, is present in gnu