replace ultra_strict with new union implementation #3910

Job	Run time
coverage	2m 14s
test-debug 3.11	49s
test 3.7	2m 5s
test-debug pypy3.10	2m 21s
test 3.8	2m 39s
test 3.9	3m 37s
rust benchmarks	4m 19s
test 3.10	5m 34s
test 3.11	2m 59s
test on ubuntu	2m 12s
test 3.12	2m 17s
test on macos	3m 53s
test pypy3.7	3m 11s
test-pydantic-integration	2m 13s
test on windows	6m 45s
test pypy3.8	2m 49s
test pypy3.9	2m 34s
test pypy3.10	2m 41s
build sdist	11s
build-wasm-emscripten	2m 26s
lint	1m 3s
build on ${{ matrix.platform \|\| matrix.os }} (${{ matrix.target }} - ${{ matrix.manylinux \|\| 'auto' }})	0s
build pgo-optimized on ${{ matrix.os }} / ${{ matrix.interpreter }}	0s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
inspect-pypi-assets	0s
check	2s
release	0s
	58m 54s

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