docs(cip): announced_eb_size is size of the txs rather than of their references

[nfrisby]

For this to be true ...

The certified_eb bit enables syncing nodes to predict the total size of valid responses to their requests for batches of EBs certified on the historical chain.

... the announced_eb_size field needs to be the size of the txs, not the size of the tx references. Syncing nodes need to download all of the txs --- there's no reason they'd already have a subset of them. And they can reconstruct the tx references from the list of txs they receive.

The MsgLeiosBlockOffer does claim a byte size for the list of references, and the peer can disconnect if the peer sends an EB body with a different size.

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This resulting scheme is a natural match for the fact that the reason an EB body contains references to txs instead of the txs themselves is merely an optimization.

[github-actions]

⚠️ CIP formatting needed - The CIP document needs formatting (TOC, figures/tables, markdown). Please run ./scripts/format-cip.sh docs/cip/README.md locally and commit the changes.

[nfrisby]

An alternative to this PR would be to leave announced_eb_size alone and add another header field announced_eb_tx_size alongside it.

[ch1bo]

Makes sense, thanks.

We should make changes to the CIP via the cardano-scaling/CIPs:leios branch, like I did with this PR

[nfrisby]

I migrated it here cardano-scaling/CIPs#13