feat(unwind): add unwind operation for sdk&greth

[AshinGau]

PR Description

feat(unwind): add unwind operation for SDK & gReth

This PR implements database unwind (rollback) support for both the execution layer (gReth) and the consensus layer (gravity-sdk), enabling operators to revert the node to a specific block height.

Execution Layer (gravity_node)

• Wires up the previously unimplemented stage unwind CLI command by adding the Commands::Stage branch in cli.rs.
• Adds an is_node_command() check in main.rs so utility subcommands (stage, db, config, etc.) bypass full node initialization (consensus, relayer), which would otherwise panic on missing config.

gravity_node stage unwind --datadir <reth-data-dir> to-block <TARGET>

Consensus Layer (gravity_cli)

• Adds ConsensusDB::unwind_to_block(target) which atomically deletes all blocks, QCs, ledger infos, epoch mappings, randomness, and stale vote/timeout certificates above the target block number.
• Introduces the gravity-cli unwind subcommand to invoke it.
• Fixes RecoveryData::find_root_by_block_number to gracefully handle missing committing QCs after an unwind by falling back to the storage ledger info, preventing "No LI found for root" panics on restart.

gravity-cli unwind --consensus-db-path <path-to-consensus-db> --target <TARGET>