Split KeyPairAlgorithm, make non-CLI part public #1286

Job	Run time
build-windows	9m 48s
Validate external types appearing in public API	1m 35s
Build rustls-cert-gen as a standalone package	26s
build (macOS-latest, stable)	47s
Measure coverage	5m 37s
build (ubuntu-latest, stable)	41s
Format & clippy	5m 21s
Documentation (stable)	1m 1s
build (ubuntu-latest, beta)	5m 31s
Documentation (nightly)	1m 8s
build (ubuntu-latest, nightly)	5m 25s
Check semver compatibility	47s
build (ubuntu-latest, stable 7 months ago)	49s
	38m 56s

Provide feedback