Generate seed once for get_beacon_proposer_index

[terencechain]

Does it make sense to move generate_seed outside of the while loop so we'd only need to compute once?

[djrtwo]

agreed seed should be outside loop but you have a bit of a bug in the current refactor.

should be

seed = generate_seed(state, current_epoch)
...
while True:
    ...
    random_byte = hash(seed + int_to_bytes8(i // 32))[i % 32]

[vbuterin]

Reminder that the spec is optimized for readability, not execution speed :)

Though I can see how this could improve readability too.