Handle breaking change with pydicom 3

[sammaxwellxyz]

recent pydicom release includes breaking change

https://github.com/pydicom/pydicom/releases/tag/v3.0.0

the install requires needs an upper bound or the code updated, a particular breaking change is the attempted use of read_file from dicom/header.py

[vsoch]

The change / fix seems pretty small - change read_file to dcmread. Would you care to PR to update the library here? We will need to do another more major bump in terms of version as well to indicate it is a breaking change.

[sammaxwellxyz]

Nice, will put that together, in the meantime I created a PR for capping the version if your prefer #267, by all means dismiss :)