avoid unnecessary serialize for RequestPacket. #319

Job	Run time
feature-checks	53s
clippy	26s
test stable --no-default-features	1m 4s
test stable	1m 4s
docs	26s
fmt	14s
test stable --all-features	1m 1s
test beta --no-default-features	40s
test beta	38s
wasm	29s
test beta --all-features	45s
test nightly --no-default-features	41s
test nightly	41s
test nightly --all-features	46s
test 1.65 --no-default-features	44s
test 1.65	52s
	11m 24s

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