Limit the size of the statement for further gossiping

[AndreiEres]

Description

Limits the size of statements that are further gossiped over the network to prevent skipping oversized messages. The limit is set to match the network protocol's MAX_STATEMENT_SIZE (256 KB), accounting for 1-byte vector length overhead because statements are sent as Vec<Statement>.

Integration

Affected crates:

• sc-statement-store: Now depends on sc-network-statement for size constants
• sc-network-statement: MAX_STATEMENT_SIZE is now public

For downstream users:

• Statements larger than 256 KB will now be rejected earlier in the validation pipeline

[AndreiEres]

/cmd prdoc --audience node_dev --bump minor

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/18339466060
Failed job name: test-linux-stable