feat: add serde for `TxType` #5404

Job	Run time
wasm-wasi	2m 58s
test ubuntu-latest stable --no-default-features	2m 8s
test ubuntu-latest stable	2m 8s
check no_std	30s
clippy	1m 5s
docs	1m 4s
test ubuntu-latest stable --all-features	2m 40s
test ubuntu-latest nightly --no-default-features	1m 9s
test ubuntu-latest nightly	1m 25s
doctest	2m 30s
feature-checks	7m 22s
fmt	16s
test ubuntu-latest nightly --all-features	2m 8s
test ubuntu-latest 1.81 --no-default-features	1m 11s
wasm-unknown	1m 57s
test ubuntu-latest 1.81	1m 29s
test windows-latest stable --no-default-features	5m 14s
test windows-latest stable	4m 56s
test windows-latest stable --all-features	6m 4s
test windows-latest nightly --no-default-features	4m 38s
test windows-latest nightly	3m 22s
test windows-latest nightly --all-features	5m 24s
test windows-latest 1.81 --no-default-features	2m 54s
test windows-latest 1.81	2m 54s
deny / cargo deny check	21s
ci success	2s
	1h 7m 49s

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