perf: cache hot PyString calls using `pyo3::intern!` macro #549

Job	Run time
style	1m 53s
tests	1m 48s
musllinux (ubuntu-22.04, i686-unknown-linux-musl, jemalloc)	1m 57s
musllinux (ubuntu-22.04, x86_64-unknown-linux-musl, jemalloc)	1m 55s
musllinux (ubuntu-22.04, armv7-unknown-linux-musleabihf, jemalloc)	1m 57s
macos (macos-13, x86_64, jemalloc)	1m 46s
musllinux (ubuntu-22.04, aarch64-unknown-linux-musl, jemalloc)	1m 56s
manylinux (ubuntu-latest, aarch64, jemalloc, crossbuild-essential-arm64, aarch64-linux-gnu-gcc, a...	1m 56s
manylinux (ubuntu-latest, x86_64, jemalloc)	1m 44s
manylinux (ubuntu-latest, x86, jemalloc, crossbuild-essential-i386, i686-linux-gnu-gcc, i686-linu...	1m 43s
macos (macos-14, aarch64, jemalloc)	1m 45s
windows (windows-latest, aarch64, mimalloc)	1m 47s
windows (windows-latest, x86, mimalloc, x86)	1m 44s
windows (windows-latest, x64, mimalloc, x64)	1m 47s
manylinux (ubuntu-latest, armv7, jemalloc, crossbuild-essential-armhf, arm-linux-gnueabihf-gcc, a...	1m 56s
sdist	19s
Release	1s
	27m 54s

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