New operator request to check sequential ordering and absence of skips.

[unit-test-sequential SEQ_Negative.xlsx](https://github.com/user-attachments/files/17979812/unit-test-sequential.SEQ_Negative.xlsx)

Problem:
The operator 'is_ordered_set' currently doesn't check skips in numbering. It does check if for example: --SEQ is completed sequentially, but it doesn't check that a number is missing in the sequence. See attached test data: LB has a number skip in --SEQ but it is not picked up if you would write:

Check:
all:
- name: --SEQ
operator: is_not_ordered_set
value: USUBJID

Possible solution
Would it be possible to create an additional operator that is an extension on 'is_ordered_set/is_not_ordered_set' so that includes checking for skips as well?