Flatten return type of symbolization #703

Job	Run time
No-op rebuilds	49s
Check generated C header	52s
Lint with clippy	52s
Benchmark	6m 6s
Test and coverage	3m 14s
Build [ubuntu-latest, 1.63.0, dev, ]	4m 6s
Test with release build	2m 16s
Build [ubuntu-latest, 1.63.0, release, ]	3m 19s
Build [ubuntu-latest, stable, dev, ]	32s
Test with address sanitizer	3m 59s
Generate documentation	24s
Build [ubuntu-latest, stable, release, ]	37s
Test with leak sanitizer	2m 33s
Build [macos-latest, 1.63.0, dev, ]	4m 2s
Build [macos-latest, 1.63.0, release, ]	4m 23s
Check code formatting	21s
Build [macos-latest, stable, dev, ]	50s
Build [macos-latest, stable, release, ]	58s
Build [ubuntu-latest, stable, dev, --no-default-features]	41s
	40m 54s

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