Add Julia implementation of `r2_score` #602

	name: Documenter
	on:
	push:
	branches: [main]
	tags: [v*]
	pull_request:

	env:
	PYTHON: "Conda" # use Julia's packaged Conda build for installing packages
	CMDSTAN_VERSION: "2.25.0"
	CMDSTAN_PATH: "${{ GITHUB.WORKSPACE }}/.cmdstan/"
	JULIA_NUM_THREADS: 2

	jobs:
	docs:
	name: Documentation
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v2
	- uses: julia-actions/setup-julia@v1
	- name: Cache CmdStan
	id: cache-cmdstan
	uses: actions/cache@v2
	with:
	path: ${{ env.CMDSTAN_PATH }}
	key: cmdstan-${{ env.CMDSTAN_VERSION }}-${{ runner.os }}
	- name: Download and build CmdStan
	if: steps.cache-cmdstan.outputs.cache-hit != 'true'
	run: \|
	wget -P ${{ env.CMDSTAN_PATH }} https://github.com/stan-dev/cmdstan/releases/download/v${{ env.CMDSTAN_VERSION }}/cmdstan-${{ env.CMDSTAN_VERSION }}.tar.gz
	tar -xzpf ${{ env.CMDSTAN_PATH }}/cmdstan-${{ env.CMDSTAN_VERSION }}.tar.gz -C ${{ env.CMDSTAN_PATH }}
	make -C ${{ env.CMDSTAN_PATH }}/cmdstan-${{ env.CMDSTAN_VERSION }}/ build
	shell: bash
	- uses: julia-actions/julia-buildpkg@latest
	- name: Setup Conda
	run: \|
	using Pkg
	Pkg.instantiate()
	using Conda
	# https://discourse.julialang.org/t/conda-not-installing-matplotlib-for-pyplot/96813/2
	Conda.add("conda==23.1.0")
	shell: julia --color=yes --project {0}
	- uses: julia-actions/julia-docdeploy@v1
	env:
	JULIA_CMDSTAN_HOME: ${{ env.CMDSTAN_PATH }}/cmdstan-${{ env.CMDSTAN_VERSION }}/ # required by CmdStan.jl
	GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
	DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }}

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