Add disproportionation reaction family support

[calvinp0]

In the current main branch, AutoTST documents that it supports Disproportionation whilst it never been fully implemented and it also does not mention that it does support Radical Addition to Multiple Bonds.

So this PR aims to:

• Registers Disproportionation with the supported family loader.
• Makes TS-group loading compatible with RMG 3.3’s Root template and AutoTST’s independent two-root TS group tree.
• Adds the correct Gaussian shell constraints for the donor-center / transferred-H / radical-acceptor coordinates (*2, *4, *1).
• Adds regression coverage for classification, distance estimation, TS geometry setup, and Gaussian shell constraints.
• Documents all four supported reaction families and corrects “Disproportination” to “Disproportionation”.

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