MetaLearners to be implemented

[kklein]

MetaLearners are a family of approaches to estimate CATEs. This issue is supposed to track which concrete MetaLearners have already been implemented in this library.

Name	Reference	Implemented?
T-Learner	https://arxiv.org/pdf/1706.03461	✅
S-Learner	https://arxiv.org/pdf/1706.03461	✅
R-Learner	https://arxiv.org/pdf/1712.04912	✅
X-Learner	https://arxiv.org/pdf/1706.03461	✅
DR-Learner	https://arxiv.org/pdf/2004.14497	✅
RA-Learner	https://arxiv.org/pdf/2101.10943
EP-Learner	https://arxiv.org/pdf/2402.01972
U-Learner	https://arxiv.org/pdf/1706.03461
F-Learner	https://arxiv.org/pdf/1706.03461
M-Learner (a.k.a PW-Learner)	https://arxiv.org/pdf/2101.10943

Please let us know if you'd like to use a MetaLearner -- whether already part of this list or not -- which is not yet implemented.