Tighten up string type representations to prevent illegal values #874

Job	Run time
Documentation (stable)	35s
Format	5s
Documentation (beta)	41s
build (macOS-latest, stable)	7m 55s
build-windows	14m 20s
build (ubuntu-latest, stable)	5m 51s
Validate external types appearing in public API	1m 14s
build (ubuntu-latest, beta)	5m 55s
Documentation (nightly)	42s
build (ubuntu-latest, nightly)	6m 12s
Clippy (--all-features)	4m 47s
Documentation (stable 7 months ago)	48s
build (ubuntu-latest, stable 7 months ago)	6m 26s
Clippy (--no-default-features --features ring)	4m 43s
Check semver compatibility	31s
Clippy (--no-default-features --features aws_lc_rs)	4m 42s
Clippy (--no-default-features --features aws_lc_rs,pem)	4m 50s
Build rustls-cert-gen as a standalone package	31s
Measure coverage	5m 34s
	1h 16m 22s

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