Fix script compare with negative number exception

[Aglargil]

Fix issue:

#832

Analysis:

In the example of nested groups in Lexy, the matching behavior is somewhat strange. Therefore, it is recommended to temporarily avoid using nested groups.
foonathan/lexy#219

Solution:

Remove nested groups and move string_concat into comparison operations. This actually aligns better with intuition, since theoretically it should be possible to perform comparison operations between two string_concat operations.

References:

https://github.com/foonathan/lexy/blob/77ba5fa5a62f16b3ab5440c6d6ef42a7cdd176bb/tests/lexy/dsl/expression.cpp#L1193-L1196
https://lexy.foonathan.net/reference/dsl/expression/#groups

[facontidavide]

thanks!