rose namelist-dump: allow (but tidy) zero-padded numeric inputs

This should allow the parsing of expressions like:
```python
&my_namelist
my_float=012.345e-00012345
```

This was not allowed before, as the number is not formally correct (zero padded implies octal on many systems). We're relaxing the restriction based on user demand - however, we will tidy the number when dumping it out.

Note that this also fixes a bug for parsing zero-padded exponent numbers without signs (unmatched group error).

@matthewrmshin, please review.