docs: updates to guide for PyO3 0.21 feedback #9246

Job	Run time
fmt	24s
check-msrv	12m 9s
semver-checks	2m 48s
python${{ matrix.python-version }}-${{ matrix.platform.python-architecture }} ${{ matrix.platform.os }} rust-${{ matrix.rust }}	0s
coverage windows-latest	3s
careful	0s
coverage macos-14	8s
coverage ubuntu-latest	15m 13s
clippy/aarch64-apple-darwin/stable	9m 10s
clippy/x86_64-unknown-linux-gnu/stable	13m 53s
docsrs	0s
clippy/powerpc64le-unknown-linux-gnu/stable	13m 4s
valgrind	0s
clippy/s390x-unknown-linux-gnu/stable	13m 3s
clippy/wasm32-wasi/stable	13m 40s
check-feature-powerset	0s
clippy/x86_64-pc-windows-msvc/stable	18m 31s
emscripten	0s
clippy/i686-pc-windows-msvc/stable	18m 33s
clippy/x86_64-unknown-linux-gnu/beta	12m 7s
test-cross-compilation ${{ matrix.os }} -> ${{ matrix.target }}	0s
test-cross-compilation-windows	0s
test-debug	0s
test-version-limits	0s
python3.12-x64 windows-latest rust-stable / build	11m 40s
python3.12-x64 macos-13 rust-stable / build	8m 45s
python3.12-x64 ubuntu-latest rust-stable / build	7m 47s
python3.12-x86 windows-latest rust-stable / build	10m 35s
python3.12-x64 ubuntu-latest rust-nightly / build	7m 28s
python3.12-arm64 macos-14 rust-stable / build	5m 33s
conclusion	1s
	3h 14m 35s

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