improve support and add tests for XA enhanced dicoms

[bpinsard]

I tried using this on XA enhanced dicoms CSA tags and can't make it work.

sds1=dcm.SharedFunctionalGroupsSequence[0][(0x0021, 0x10FE)][0]
mrprot = sds1.get((0x0021, 0x1019))
parsed_csa = CsaHeader(mrprot.value).read()

CsaReadError: CSA element #0 has an invalid check bit value: 1632648224!
Valid values are {205, 77}

Could use https://github.com/neurolabusc/dcm_qa_xa30/tree/main/In and https://github.com/neurolabusc/dcm_qa_xa60/tree/main/In as test dicoms.

[ZviBaratz]

I'm sorry, @bpinsard, but the package isn't currently maintained. Very happy to accept PRs 🙏