migration to pyo3 0.21 new `Bound` API #810

Job	Run time
check-msrv	41s
lint	5s
examples	1m 30s
coverage	0s
cross-build	0s
careful	0s
python${{ matrix.python-version }}-${{ matrix.platform.python-architecture }} ${{ matrix.platform.os }}	0s
valgrind	0s
	2m 16s

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