Cold protein split method about tdc

[kexinhuang12345]

Hi @agamemnonc, the current cold protein split is from the general cold start split (https://zitniklab.hms.harvard.edu/TDC/functions/data_split/#cold-start-split). It is basically for pair data such as drug-target protein interaction data, where we first split on protein and then map all DTI pairs. This means it tests on unseen proteins.

But we are indeed looking for more realistic split methods. Do you have a pointer for what split you want to include? or feel free to make a PR. Thanks!