Simplify OptionalWrapper #821

Job	Run time
Build & Test (fancy, 1.70.0, ubuntu-latest)	45s
Check fmt & build docs	19s
Build & Test (fancy, 1.70.0, macOS-latest)	1m 38s
Minimal versions check (ubuntu-latest)	19s
Miri	3m 10s
Build & Test (fancy, 1.70.0, windows-latest)	1m 14s
Minimal versions check (macOS-latest)	30s
Build & Test (fancy, stable, ubuntu-latest)	37s
Minimal versions check (windows-latest)	33s
Build & Test (fancy, stable, macOS-latest)	59s
Build & Test (fancy, stable, windows-latest)	1m 54s
Build & Test (syntect-highlighter, stable, ubuntu-latest)	52s
Build & Test (syntect-highlighter, stable, macOS-latest)	4m 28s
Build & Test (syntect-highlighter, stable, windows-latest)	1m 58s
	19m 16s

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