Improve performance of inactive tracing spans #532

Job	Run time
minimal-versions	2m 46s
Doc checks	1m 31s
Cargo deny checks	33s
Check unstable	1m 35s
Check feature combinations (ubuntu-latest)	3m 12s
Test unstable	2m 15s
Check feature combinations (macos-latest)	3m 44s
Run example (dry run)	1m 45s
fmt	14s
Clippy checks	1m 23s
Test (aarch64-ios)	1m 19s
Test (arm64-android)	1m 10s
Test (aarch64-linux)	2m 15s
Test (arm-android)	1m 13s
Test (x86_64-windows)	2m 51s
Test (x86_64-macos)	2m 50s
Test (x86_64-linux)	2m 51s
Pull Request Status Checks	0s
	33m 27s

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