ensure default serial generation fits 20 bytes #730

Job	Run time
Format	6s
Validate external types appearing in public API	1m 18s
build (macOS-latest, stable)	46s
build-windows	8m 6s
build (ubuntu-latest, stable)	5m 23s
Clippy	4m 54s
build (ubuntu-latest, beta)	5m 11s
Documentation (stable)	33s
build (ubuntu-latest, nightly)	5m 24s
Check semver compatibility	28s
Documentation (beta)	40s
build (ubuntu-latest, stable 7 months ago)	35s
Documentation (nightly)	39s
Documentation (stable 7 months ago)	42s
Measure coverage	29s
	35m 14s

Provide feedback