feat(eips): Make prague field an enum #5095

Job	Run time
doctest	2m 17s
wasm-unknown	1m 16s
clippy	1m 0s
check no_std	20s
docs	1m 4s
feature-checks	6m 4s
fmt	16s
wasm-wasi	1m 22s
test ubuntu-latest stable --no-default-features	1m 58s
test ubuntu-latest stable	2m 1s
test ubuntu-latest stable --all-features	2m 38s
test ubuntu-latest nightly --no-default-features	1m 23s
test ubuntu-latest nightly	1m 29s
test ubuntu-latest nightly --all-features	2m 12s
test ubuntu-latest 1.79 --no-default-features	1m 18s
test ubuntu-latest 1.79	1m 10s
test windows-latest stable --no-default-features	3m 44s
test windows-latest stable	4m 51s
test windows-latest stable --all-features	5m 10s
test windows-latest nightly --no-default-features	3m 37s
test windows-latest nightly	4m 9s
test windows-latest nightly --all-features	5m 5s
test windows-latest 1.79 --no-default-features	2m 15s
test windows-latest 1.79	2m 40s
ci success	4s
	59m 23s

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