Update JHU and Canon phantom conversions

[bilgelm]

Made updates to *_conversions.* for JHU and Canon metadata. Added "3D Reprojection" to PET_reconstruction_methods.json.

Notes:

• ecat2bids doesn’t respect user specified InjectedRadioactivityUnits of "mCi" and overrides it as “MBq”. (Similar issue with SpecificRadioactivityUnits.) Tried to figure out why this was happening, but was unsuccessful (this issue doesn’t happen with dcm2niix4pet). So my Siemens HRRT json generated with python_conversions.py is incorrect, but the kwargs values in the .py are correct.
• Decided to use "3D Reprojection" rather than "3D Kinahan-Rogers", since the former seems to be more common in the literature.
• Haven't tested/inspected the matlab conversions.

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📚 Documentation preview 📚: https://pet2bids--281.org.readthedocs.build/en/281/

[bendhouseart]

ecat2bids doesn’t respect user specified InjectedRadioactivityUnits of "mCi" and overrides it as “MBq”. (Similar issue with SpecificRadioactivityUnits.) Tried to figure out why this was happening, but was unsuccessful (this issue doesn’t happen with dcm2niix4pet). So my Siemens HRRT json generated with python_conversions.py is incorrect, but the kwargs values in the .py are correct.

It's a tricky dance as we want to respect what the user provides while also getting some of the units/conversions right. But as to why ecat2bids differs from dcm2niix4pet in this manner is most likely due to an implementation error on my part.

I'm also a bit confused as to why the phantoms ci isn't running on this PR....will clone and run make testphantoms and if all is hunky dory merge and close this PR.