proto: Reject RetryToken with extra bytes #5317

Job	Run time
test on netbsd	4m 49s
test on illumos	6m 44s
test (ubuntu-latest, stable)	1m 38s
test on freebsd	3m 50s
test (ubuntu-latest, beta)	1m 33s
test on solaris	13m 40s
test (macos-latest, stable)	1m 8s
audit	25s
features (ubuntu-latest)	1h 20m 13s
test (windows-latest, stable)	2m 53s
lint	1m 7s
features (macos-latest)	25m 50s
msrv	1m 9s
features (windows-latest)	50m 57s
test-aws-lc-rs	1m 45s
test-android (x86_64-linux-android, x86_64, 26)	3m 0s
test wasm32-unknown-unknown	58s
test-android (x86_64-linux-android, x86_64, 25)	2m 37s
test-android (i686-linux-android, x86, 26)	2m 55s
test-android (i686-linux-android, x86, 25)	2m 28s
	3h 29m 39s

Provide feedback