Make reftest generation reproducible

[jtraglia]

It appears that there are still some differences when you run make reftests on the same commit but different systems. This is almost certainly related to randomness somewhere. It appears to exist in these different areas:

• ssz_generic/progressive_containers/invalid/*modded*
• sanity/blocks/pyspec_tests/mix_blob_tx_and_non_blob_tx
• operations/proposer_slashing/pyspec_tests/builder_payment_deletion_current_epoch
• operations/proposer_slashing/pyspec_tests/builder_payment_deletion_previous_epoch
• operations/proposer_slashing/pyspec_tests/builder_payment_deletion_too_late

[anumukul]

Hi @jtraglia , I’d like to take this issue and can deliver a fix within 24 hours.
I’ve worked on similar projects before and have relevant experience, so I should be able to handle this efficiently.

[anumukul]

please review my PR @jtraglia