chore(consensus): add `Transaction::size` into trait `Transaction` #4304

Job	Run time
doctest	22s
test ubuntu-latest stable --no-default-features	23s
test ubuntu-latest stable	23s
test ubuntu-latest stable --all-features	37s
test ubuntu-latest nightly --no-default-features	50s
check no_std	17s
clippy	32s
test ubuntu-latest nightly	56s
test ubuntu-latest nightly --all-features	1m 5s
docs	1m 1s
test ubuntu-latest 1.79 --no-default-features	35s
feature-checks	15s
test ubuntu-latest 1.79	43s
wasm-unknown	40s
test windows-latest stable --no-default-features	2m 36s
wasm-wasi	17s
test windows-latest stable	3m 7s
test windows-latest stable --all-features	3m 5s
cfg-check	44s
test windows-latest nightly --no-default-features	2m 33s
test windows-latest nightly	2m 33s
test windows-latest nightly --all-features	2m 58s
test windows-latest 1.79 --no-default-features	1m 45s
fmt	12s
test windows-latest 1.79	2m 28s
	30m 57s

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