Add tests for hexBinary

[ajnelson-nist]

References:

• [AC-139] FAQ question - Does CASE require hex data be entered
  uppercase or lowercase?

Signed-off-by: Alex Nelson alexander.nelson@nist.gov

[ajnelson-nist]

@asovern-mitre , this branch is ready for your review in support of a website FAQ item, and potentially a data-policy change proposal for UCO.

• As a style matter, is it OK with you for these tests to use the xfail design? See e.g. lines 1460 and 1462.
• Does this hexbinary test also need to add some explicit items about testing JSON as not-JSON-LD?

[asovern-mitre]

@asovern-mitre , this branch is ready for your review in support of a website FAQ item, and potentially a data-policy change proposal for UCO.

* As a style matter, is it OK with you for these tests to use the xfail design?  See e.g. lines [1460](https://github.com/casework/CASE-Utilities-Python/pull/4/checks?check_run_id=2546928748#step:6:1460) and [1462](https://github.com/casework/CASE-Utilities-Python/pull/4/checks?check_run_id=2546928748#step:6:1462).

* Does this hexbinary test also need to add some explicit items about testing JSON as not-JSON-LD?

Styling looks fine to to me, as for the explicit testing in JSON vs not-JSON-LD, I don't think we need to do that at this time. The content in the PR seems good for now.