Addition of Asserts for special data types XINT, UXINT, XWORD?

### Discussed in https://github.com/tcunit/TcUnit/discussions/164

<div type='discussions-op-text'>

<sup>Originally posted by **AndyP01** October  8, 2021</sup>
Could it be beneficial to add asserts for the special data types XINT, UXINT and XWORD?

See here:
https://infosys.beckhoff.com/english.php?content=../content/1033/tc3_plc_intro/2529448075.html&id=</div>