Revamp type descriptors #309

Job	Run time
Address sanitizer	1m 31s
rustfmt	1m 38s
static builds (ubuntu-latest, stable)	1m 24s
conda (ubuntu, conda-forge, stable)	48s
static builds (windows-latest, stable-msvc)	5m 45s
conda (windows, conda-forge, stable)	2m 30s
static builds (windows-latest, stable-gnu)	5m 50s
test apt (stable)	34s
conda (macos, conda-forge, stable)	2m 3s
static builds (macos-11, stable)	4m 9s
test apt (beta)	44s
static builds (macos-latest, stable)	1m 54s
test apt (nightly)	44s
	29m 34s

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