Treat position bias via GAM in LambdaMART #7143

Job	Run time
r-package (debian, R-devel, clang)	5m 36s
r-sanitizers (ubuntu-latest, R-devel, gcc ASAN/UBSAN)	5m 36s
r-sanitizers (ubuntu-latest, R-devel, clang ASAN/UBSAN)	5m 35s
r-package (ubuntu-latest, gcc, R 3.6, cmake)	5m 37s
r-package (ubuntu-latest, gcc, R 4.2, cmake)	5m 37s
r-package (ubuntu-latest, clang, R 3.6, cmake)	1m 35s
r-package (ubuntu-latest, clang, R 4.2, cmake)	5m 38s
r-package (macOS-latest, gcc, R 4.2, cmake)	5m 42s
r-package (macOS-latest, clang, R 4.2, cmake)	5m 42s
r-package (windows-latest, MINGW, R 3.6, cmake)	6m 42s
r-package (windows-latest, MINGW, R 4.2, cmake)	5m 31s
r-package (windows-2019, MSVC, R 3.6, cmake)	5m 35s
r-package (windows-2022, MSVC, R 4.2, cmake)	5m 35s
r-package (windows-latest, MINGW, R 3.6, cran)	5m 36s
r-package (windows-latest, MINGW, R 4.2, cran)	5m 35s
r-package (ubuntu-latest, gcc, R 4.2, cran)	5m 35s
r-package (macOS-latest, clang, R 4.2, cran)	5m 42s
r-rchk (ubuntu-latest, gcc, R 4.2, cran)	5m 37s
all-r-package-jobs-successful	3s
	1h 38m 9s

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