API: support roots as `dict` in `dump()`, `load()` #81

	---
	# configuration for GitHub Actions
	name: dd tests
	on:
	push:
	pull_request:
	schedule:
	- cron: '37 5 5 * *'
	jobs:
	build:
	name: Build
	runs-on: ubuntu-22.04
	strategy:
	matrix:
	python-version: [
	'3.11',
	]
	steps:
	- uses: actions/checkout@v2
	- name: Set up Python ${{ matrix.python-version }}
	uses: actions/setup-python@v2
	with:
	python-version: ${{ matrix.python-version }}
	- name: Prepare installation environment
	run: \|
	./.github/workflows/setup_build_env.sh
	- name: Install `dd`
	run: \|
	set -o posix
	echo "Exported environment variables:"
	export -p
	export \
	DD_FETCH=1 \
	DD_CUDD=1 \
	DD_CUDD_ZDD=1 \
	DD_SYLVAN=1
	pip install . \
	--verbose \
	--use-pep517 \
	--no-build-isolation
	- name: Install test dependencies
	run: \|
	pip install pytest
	- name: Run `dd` tests
	run: \|
	set -o posix
	echo "Exported environment variables:"
	export -p
	# run tests
	make test
	- name: Run `dd` examples
	run: \|
	pushd examples/
	python _test_examples.py
	popd

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