Fix element-wise comparison for grad_lib_values in write_seq.py

[josalggui]

Description

This pull request fixes an issue with element-wise comparison in the write_seq.py code.

Problem

The original code compares the entire list grad_lib_values to the string 'g', which results in False instead of an element-wise comparison in some cases depending on python or libraries versions. When if any(arb_grad_mask) is called, False gives rise an error, while an empty list works properly.

Solution

Updated the code to use a list comprehension to perform element-wise comparison:

arb_grad_mask = [value == 'g' for value in grad_lib_values]
trap_grad_mask = [value == 't' for value in grad_lib_values]