Support Literal and Union/Optional types on structs. Fixes #405 #1308

Job	Run time
initialize	33s
lint (ubuntu-24.04, 3.9)	48s
build_sdist (ubuntu-24.04, 3.9)	48s
build (ubuntu-24.04, 3.8, cp38, false)	34m 28s
build (ubuntu-24.04, 3.9, cp39, false)	33m 38s
build (ubuntu-24.04, 3.10, cp310, false)	33m 34s
build (ubuntu-24.04, 3.11, cp311, false)	32m 35s
build (ubuntu-24.04, 3.12, cp312, false)	35m 25s
build (macos-14, 3.11, cp311, false)	19m 15s
build (macos-14, 3.12, cp312, false)	22m 58s
build (windows-2019, 3.12, cp312, false)	1h 6m 58s
test_sdist	0s
test (ubuntu-24.04, 3.8, false)	2m 31s
test_dependencies (ubuntu-20.04, 3.9, sqlalchemy<2)	1m 3s
test (ubuntu-24.04, 3.9, false)	2m 10s
test_dependencies (ubuntu-20.04, 3.9, numpy==1.22.4)	2m 14s
test (ubuntu-24.04, 3.10, false)	2m 16s
test_dependencies (ubuntu-20.04, 3.9, perspective-python<3)	1m 6s
test (ubuntu-24.04, 3.11, false)	2m 4s
test (ubuntu-24.04, 3.12, false)	2m 14s
test (macos-14, 3.11, false)	3m 8s
test (macos-14, 3.12, false)	2m 59s
test (windows-2019, 3.12, false)	5m 4s
publish_release_artifacts	0s
	5h 7m 49s

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