Fix `pyo3` as an optional dependency #668

Job	Run time
build on ${{ matrix.os }} (${{ matrix.target }} - ${{ matrix.interpreter \|\| 'all' }}${{ (((matrix.os == 'linux') && format(' - {0}', (((matrix.manylinux == 'auto') && 'manylinux') \|\| matrix.manylinux))) \|\| '') }})	0s
build sdist	23s
bench	1m 19s
build pgo-optimized on ${{ matrix.os }} / ${{ matrix.interpreter }}	0s
fuzz on ubuntu-latest	6m 6s
fuzz skip	6m 3s
lint	1m 22s
fuzz on macos-latest-xlarge	45m 1s
resolve	11s
test on macos-latest	1m 5s
test jiter-python	55s
test on macos-latest-xlarge	51s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
test rust-stable on linux	1m 3s
test rust-nightly on linux	1m 49s
test rust-1.75 on linux	1m 9s
inspect-pypi-assets	0s
check	1s
release	0s
release-python	0s
	1h 7m 18s

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