add Bound::as_unbound #9073

Job	Run time
fmt	14s
python${{ matrix.python-version }}-${{ matrix.platform.python-architecture }} ${{ matrix.platform.os }} rust-${{ matrix.rust }}	0s
check-feature-powerset	0s
careful	0s
check-msrv	11m 11s
coverage-windows	8s
docsrs	0s
coverage-macos	10s
coverage-ubuntu	15m 28s
emscripten	0s
semver-checks	30s
test-cross-compilation ${{ matrix.os }} -> ${{ matrix.target }}	0s
test-cross-compilation-windows	0s
test-debug	11m 8s
clippy/x86_64-apple-darwin/stable	18m 35s
test-version-limits	0s
clippy/x86_64-unknown-linux-gnu/stable	13m 46s
valgrind	0s
clippy/powerpc64le-unknown-linux-gnu/stable	12m 4s
clippy/s390x-unknown-linux-gnu/stable	13m 9s
clippy/wasm32-wasi/stable	12m 34s
clippy/x86_64-pc-windows-msvc/stable	17m 11s
clippy/i686-pc-windows-msvc/stable	17m 3s
clippy/x86_64-unknown-linux-gnu/beta	12m 0s
python3.12-x64 ubuntu-latest rust-stable / build	7m 33s
python3.12-x64 windows-latest rust-stable / build	12m 43s
python3.12-x86 windows-latest rust-stable / build	13m 56s
python3.12-x64 ubuntu-latest rust-nightly / build	7m 36s
python3.12-x64 macos-latest rust-stable / build	10m 2s
conclusion	3s
	3h 27m 4s

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