Bin txs into shreds without breaking them

[behzadnouri]

So that the receiver can do sig-verify out of order.

• Need to confirm metadata/header would not tip the size over MTU limit for current mainnet txs.
• Figure out how to maintain forward/backward compatibility at switching point across cluster.

https://discord.com/channels/428295358100013066/478692221441409024/822602147199582229
https://discord.com/channels/428295358100013066/478692221441409024/870088483388137482

we can change the format of the shred to be a list of full TXs
with some metadata on entry and order in that entry if we need to bin them out of order for efficiency

we might have to quietly lower the size and hope no one currently running is impacted
at some point, we should add stored TXs where users can upload a bigger tx into an account and execute it
that would also let VMs continue large computations

Also for reference: #17102

[aeyakovenko]

It's effective even if it's not done for 100% of the TXs. so the few that trip the MTU size header can be split.

[steviez]

Think this one and #16403 have similar intentions