add device<->host transfer mappers (#282) #1646

Job	Run time
Typos	6s
Pylint	1m 37s
Mypy	1m 42s
Ruff	8s
Documentation	1m 49s
Examples Conda Py3	1m 19s
Tests for downstream project meshmode	12m 36s
Pytest Conda Py3 Intel	2m 2s
Tests for downstream project grudge	10m 26s
Pytest Conda Py3 POCL	2m 29s
Tests for downstream project mirgecom	4s
Tests for downstream project mirgecom_examples	3s
	34m 21s

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