Factor out `IncomingToken` #5232

Job	Run time
test on netbsd	4m 50s
test on netbsd	4m 50s
test on freebsd	6h 0m 1s
test on freebsd	4m 2s
test (ubuntu-latest, stable)	1m 53s
test (ubuntu-latest, stable)	1m 53s
test on illumos	11m 42s
test on illumos	11m 42s
test (ubuntu-latest, beta)	1m 18s
test (ubuntu-latest, beta)	1m 18s
test-aws-lc-rs	2m 3s
test-aws-lc-rs	2m 3s
test on solaris	5m 40s
test on solaris	5m 40s
test (macos-latest, stable)	1m 17s
test (macos-latest, stable)	1m 17s
test (windows-latest, stable)	5m 0s
test (windows-latest, stable)	5m 0s
test wasm32-unknown-unknown	1m 6s
test wasm32-unknown-unknown	1m 6s
audit	25s
audit	25s
features (ubuntu-latest)	1h 21m 1s
features (ubuntu-latest)	1h 21m 1s
lint	1m 26s
lint	1m 26s
features (macos-latest)	32m 8s
features (macos-latest)	32m 8s
msrv	1m 18s
msrv	1m 18s
features (windows-latest)	51m 30s
features (windows-latest)	51m 30s
test-android (x86_64-linux-android, x86_64, 26)	3m 12s
test-android (x86_64-linux-android, x86_64, 26)	3m 12s
test-android (x86_64-linux-android, x86_64, 25)	3m 1s
test-android (x86_64-linux-android, x86_64, 25)	3m 1s
test-android (i686-linux-android, x86, 26)	2m 56s
test-android (i686-linux-android, x86, 26)	2m 56s
test-android (i686-linux-android, x86, 25)	2m 48s
test-android (i686-linux-android, x86, 25)	2m 48s
	13h 13m 11s

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