chore: set relay parent offset to 1

[ipapandinas]

Pull Request Summary

This PR set the relay parent offset to 1 to reduce the collation latency when relay chain forks appear. It adds small extra inherent overhead increasing slightly the PoV size and adding an extra 6sec delay to XCM processing (12sec expected latency). However this configuration will improve block time stability.

Note: Offset is hardcoded to 0 in the parachain system pallet while collators migrate to the slot_based Aura consensus to prevent any runtime panic when trying to validate descendants blocks missing in the inherent.

[github-actions]

Package	Line Rate	Branch Rate	Health
primitives/src/xcm	66%	0%	➖
pallets/dapp-staking/src/test	0%	0%	❌
pallets/dynamic-evm-base-fee/src	84%	0%	✔
pallets/collator-selection/src	82%	0%	✔
pallets/vesting-mbm/src	87%	0%	✔
precompiles/dispatch-lockdrop/src	89%	0%	✔
pallets/astar-xcm-benchmarks/src/generic	100%	0%	✔
pallets/dapp-staking/rpc/runtime-api/src	0%	0%	❌
precompiles/substrate-ecdsa/src	74%	0%	➖
pallets/unified-accounts/src	79%	0%	➖
pallets/astar-xcm-benchmarks/src/fungible	100%	0%	✔
precompiles/assets-erc20/src	77%	0%	➖
pallets/inflation/src	58%	0%	➖
primitives/src	55%	0%	➖
chain-extensions/types/unified-accounts/src	0%	0%	❌
chain-extensions/types/assets/src	0%	0%	❌
chain-extensions/unified-accounts/src	0%	0%	❌
precompiles/xcm/src	70%	0%	➖
precompiles/dapp-staking/src	89%	0%	✔
pallets/democracy-mbm/src	30%	0%	❌
pallets/ethereum-checked/src	76%	0%	➖
pallets/dapp-staking/src	83%	0%	✔
precompiles/dapp-staking/src/test	0%	0%	❌
pallets/xc-asset-config/src	57%	0%	➖
chain-extensions/pallet-assets/src	55%	0%	➖
precompiles/unified-accounts/src	100%	0%	✔
pallets/astar-xcm-benchmarks/src	86%	0%	✔
precompiles/sr25519/src	69%	0%	➖
pallets/collective-proxy/src	94%	0%	✔
pallets/dapp-staking/src/benchmarking	94%	0%	✔
Summary	73% (3727 / 5087)	0% (0 / 0)	➖

Minimum allowed line rate is 50%